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ANALOG DEVICES AD1170 handbook

1. 0 O 2x Tieall Sms Set integration Time to Arbitrary Value Resat AD 1170 to Power Up Conditions Messure the Offset Voltage Value at the AD1170 Input and Store NULEN Subtract NULL Measured Value from All Subsequent Conversions NULD Cancel the Effect of the NULEN Command CALEN 10110000 CALEN CALibration ENable enables automatic background calibration cycling In this mode background calibration cycles are executed automatically whenever the AD1170 is not otherwise occupied If a command is received during a calibration cycle that cycle will be aborted and the command will be executed CALDI 10111000 CALDI CALibration Disable disables automatic background calibration After executing this command the AD1170 will be completely idle between commands While in this state 2 single calibration cycle may be invoked with the SCAL command CNV 00001000 CNV CoNVert causes a single conversion to be performed using the current default integration time and data format CNVP 00010C C CNVP CoNVert using specific Preset time causes a single conversion to be performed using one of the cight preset inte gration times as listed in Figure 10 The default integration time is not changed The three bit code for the desired integration time is embedded in the lowest three bits of the command code ECAL 00011000 ECAL Electronic CALibration causes an electronic calibration cycle to be performed An external 5 volt referen
2. SCAL Single CALibration performs a single background cali bration cycle This command is intended for use when auto matic background calibration has been disabled via the CALDI command 10 SDC 01000C SDC Set Default Calibration time sets the default calibration time Tcal according to the three bit code embedded in the lowest three bits of the command The calibration times are shown in Figure 10 Note that the actual duration of a calibration cycle is approximately 2 x T cal 9 milliseconds WRNV 10011A A Ap WRNV WRite NonVolatile writes the user supplied data in the PARAMETER and PARAMETER 2 registers into the user accessible area of the AD1170 s nonvolatile memory Eight words of this memory are available and are addressed by the lowest three bits of the command RDNV 10100A A RDNV ReaD Non Volatile reads one word from the user ac cessible portion of the nonvolatile memory within the AD1170 and places the data into the LOW DATA and MID DATA registers for retrieval by the user The address of the desired word is embedded into the lowest three bits of the command RST 10010000 RST ReSeT is effectively equivalent to a hardware reset of the AD1170 After executing this command all nonvolatile parameters including the ECAL coefficient the default integration and calibration periods EIS ELS period NULL value and the default format will be restored to their last saved values automatic calibration will be e
3. When the AD1170 is triggered to perform a conversion two seperate phases are performed first an integration phase where the input signal is actually measured and then a computation phase where the data from the integration phase is processed along with both the volatile and nonvolatile calibration data and formatted for output as the user desires The duration of the integration phase can be programmed by the user and may be as short as one millisecond or as long as 350 milliseconds The computation phase always lasts approxi mately three milliseconds and commences immediately after the integration phase is over Therefore the total conversion time will equal the user programmed integrate time plus a fixed 3 milliseconds Status signals are provided to indicate when the data is ready and when the converter may be retriggered for the next conversion For maximum stability the AD1170 periodically calibrates itself by performing measurements upon a zero input signal and a full scale signal provided by the internal reference This technique cancels any drift within the charge balancing converter itself resulting in negligible offset drift and gain stability equal to that of the reference Calibration cycles may be programmed to take place whenever the AD1170 is idle or they may be invoked under system control p twe tesm tens cs ue Ah AQ A1 q z E Gece Me why WRITE CYCLE TIMING REQUIREMENTS PARAMETER DE
4. the user invokes a SAVA command which will save this coefficient along with the other nonvolatile parameters in the nonvolatile memory chip When the module is powered up the previously saved coefficient is recalled from nonvolatile memory and stored in random access memory In order to use the ECAL command the input to the AD1170 must first be presented with an external 5 volt reference standard such as is usually found in many calibration labs The ECAL command may then be invoked the external reference voltage must remain at the input until command execution is complete If the calibration is to be made nonvolatile a SAVA command must then be invoked ECAL may also be used as a means of making limited ratiometric measurements For example in some applications it may be uscful to be able to measurc the output of some transducer with respect to its excitation if the excitation can be scaled to the range of 4 5 to 5 5 volts then it can be used as an excitation for the ECAL process Having digitized the excitation all subsequent conversions will be ratioed to the ECAL value For example if an ECAL procedure is performed upon a 4 5 volt source and the converter subsequently digitizes a 2 25 volt signal the converter output will be half of full scale or 11000 assuming offset binary coding The converter can be restored tu absolute cali bration by executing a RESA command which will restore the last nonvolatile ECAL coeffic
5. HIGH DATA byte will be filled with the value of the MSB _6 REV A AD1170 PROGRAMMING THE INTEGRATION PERIOD The key parameter of any integrating A D converter is the integration period As shown in Figure 9 an intcgrating A D converter provides maximum normal mode rejection at those frequencies which are integral multiples of 1 T int where T int is the integration period The most common way to exploit this characteristic is to set the integration period equal to one period of the power line frequency so that ac hum will be rejected Relative frequency f log sesle RM 107 Figure 9 Normal Mode Rejection The duration of the integration also affects the resulting resolution of the data long integration times result in more usable resolution than do short integration periods The AD1170 unlike most dual slope converters offers the user the capability of programming the integration time This feature can be uscd to great advantage in systems design since the integration time can be optimized for differing system conditions For example in systems whose inputs are severely polluted by 60Hz noise the user may wish to program the AD1170 for a 100 millisecond integration time which will result in excclicnt 60Hz normal mode rejection In another application a user may wish to scan a large number of channels rapidly looking for gross input changes then slow down in order to make a high resolution con
6. any external reference voltage must be an essentially static DC signal INTERFACING TO THE AD1170 The AD1170 contains an cight bit microproccssor compatible interface structure including control lines It can be interfaced to any microprocessor based system in either a memory mapped or F O mapped mode and occupies four successive bytes of read write address space as shown in Figure 6 es m5 wa as ao runction rH x x x x DeviceNotSelected Unused H il Parameter 2 Write e H E i t CommadWrite pu te uw rH H HighDataRead t t TR TH t MidDataRead e fe W E H towDataRead ipe te e e i sauene X DON T CARE Figure 6 Control Functions Actempting to READ and WRITE at the same time RD and WR set low may alter the contents of the internal nonvolatile memory AD1170 The AD1170 is controlled by writing a command into the lowest byte of the device image Upon receipt of the command byte the BUSY line is set low indicating that command interpretation is in progress The BUSY line returns high following command interpretation and a command dependent execution time This signals that the command execution has been completed and another command may now be written The logical inverse of the BUSY linc is available in the STATUS byte for use in polling See the section below about THE STATUS BYTE When the command requires one or two parameters in add
7. cycles and their duration The duration of the calibration cycle is an important parametcr because it affects the accuracy of the calibration cycle itself Errors in the calibration cycle appear in the output data as instantaneous offset and span errors If automatic background calibration is enabled these errors effectively appear as noise Just as in the case of input conversions longer calibration umes result in more accuracy and less noise Of course there may be system applications where there simply isn t sufficient time to perform a long calibration cycle For this reason the AD1170 offers the user the ability to specify the calibration period using the SDC command The argument for the SDC command is the same three bit code as is used for the SDI and CNVP commands The reason for See the section titled The AD1170 Command Set for the formula used to compute the proper binary value Caution is advised if no signal is present at the ELS input when the ELS command is executed or if the signal is not within acceptable frequency limits the module may hang and require a hardware reset to continue operation FS AD1170 this is that each calibration cycle consists essentially of two ordinary conversion cycles performed upon the internal zero and span references For example if an SDC command with an argument of 3 is executed the default calibration time will then be approximately 49 millisecond
8. such as the integration period output data format calibration coefficient etc The AD1170 is calibrated at the factory with the following default senings FORMAT 16 bit offset binary DEFAULT T int 16 667 milliseconds code 2 DEFAULT Tical 100 milliseconds code 4 AD1170 ARCHITECTURAL OVERVIEW The AD1170 is a complete microcomputer based measurement subsystem containing three major elements a highly precise charge balancing converter a single chip microcomputer and a custom CMOS controller chip The heart of the measurement technique is the charge balancing converter essentially a voltage to frequency converter This converter measures the input signal by balancing a proportional current against a train of precisely controlled reference current pulses using an integrator The microprocessor together with the counting and gating circuitry within the CMOS controller chip measures the period of the reference current pulses by interpolating them using a 12MHz clock signal The resulting BE E I Juk Ab Al twat a a 00 07 READ CYCLE TIMING REQUIREMENTS PARAMETER DESCRIPTION WIN TYP MAK UNITS to AD Pulse Width 150 m kon Chip Select to RD Low 0 ns tens Chip Select Hold Time d ns las Address Setup Time 10 ns Tan Address Hold Time nS toav Date Valid Time 100 m ton Data Hold Time so ne data is converted to binary representation by the use of floating point firmware routines within the microprocessor
9. 170 is inserted directly into an AC5004 board which is designed to plug into the backplane of an IBM PC XT AT Thus armed with an IBM PC an AD1170 and an ACS004 evaluation board the user is fully prepared to examine the operation of the AD1170 A User s Manual provides all the information required to put the AC5004 AD1170 evaluation process into operation In the manual are full descriptions of the ACS004 memory address and power source selection jumpers as well as a schematic documenting the interface of the AD1170 to a computer bus The package also contains a comprehensive demonstration program written in BASIC that completely exercises all the functions of the AD1170 The AC5004 is an accessory that will make readily available to the user all the tools needed to comprehensively test the AD1170 PRODUCT HIGHLIGHTS 1 ACS004 plugs directly into IBM PC XT AT or compatibles Standard short slot card size 5 7 8 x 5 x 1 2 The ACS004 enables the user to evaluate the AD1170 high resolution programmable integrating A D converter without having to build a bread board or prototype 3 The evaluation boards come complete with software and programming examples designed to exercise all of the AD1170 s functions 4 ACS004 schematic and assembly drawings are provided to be used as examples of how to interface the AD1170 to a micro processor bus Please note Order AC5004 does not include AD1170
10. AD1170 is interfaced in the I O space the DIP switch controls the specific location of the AD1170 within the available address Figure 12 IBM PC XT to AD1170 interface INTERFACING TO AN 8851 MICROCONTROLLER Figure 13 shows how an AD1170 may be interfaced to an 805 microcontroller using a technique commonly called byte bang ing where the control lines and data bus of a device are man ipulated under firmware control This byte banging technique can be adapted to most microprocessors and is useful in situations where a conventional bus structurc is cither nonexistent or unavailable for use The AD1170 s data bus is connected to the 8051 using I O lines P2 0 through P2 7 The address lines AO and Al are connected to LO lines P1 0 and P1 1 respectively The RD and WR lines are connected to P1 2 and P1 3 The CS line of the AD1170 is grounded when it is the only device connected to the 8051 but multiple AD1170s could easily be connected in the same way if each CS line were separately controlled Note that che 8051 microcontroller does contain a conventional bus structure the byte benging interface shown here is presented as an example of an alternative technique Figure 13 Simple 8051 to AD1170 interface To initialize the interface first write 1 s to the port pins connected to the data bus and the RD and WR control lines This puts the 8051 I O lines into a lightly pulled up statc simu
11. Figure 10 Preset integration Periods The third way to set the integration period is via the external line sampling feature using the ELS command This command samples the period of the logic signal presented to the ELS input pin Pin 12 and sets the externally definable period register accordingly This feature is most useful in environments with fluctuating line frequencies By executing an occasional ELS command the converter effectively tracks the line fre quency To use this feature a cican bounce free logic represen tation of the line frequency must be present at the ELS input during the execution of the ELS command Once having performed the ELS command the measured integration time may be selected using the SDI or CNVP commands along with the HHH code from the table in Figure 10 It should be noted that the actual integration period used in the measurement process is accurate to about 200ps due to the limitations of the charge balancing converter This is adequate however for greater than SOdB of normal mode rejection at 60Hz when using an integration period of 1 60 second Even greater normal mode rejection may be obtained when the inte gration period is a multiple of the line frequency period CONTROLLING THE CALIBRATION CYCLE The ADI170 achieves its excellent span and offset stability by calibrating itsclf against its internal reference voltages The user can control the frequency of occurrence for calibration
12. ME to60ppm SPAN to 20ppm SPAN ii o by i 2 2 ra 3 TEMPERATURE RANGE Rated Performance 0 70 Storage 25 85 ga SIZE 1 24 x 2 5 x 0 55 max 31 4 x 63 5 x 14 0 mm NOTES The ursbie resolution is limized by noise which is largely determined by the integration period and calihrenon peniad Consult the chart in Figure 4 for typical peak to peak noise versus inlegration and calibratina perind The integral linearity is defined as the deviation from a straight line drawn herween the endpoiars of the converter This specification is independent of gaia andor offset errors 1000 Tuim 3 milliseconds Where Tint is cxpresecd ia number of milliseconds Specifications subject 10 change withou notice IBM PCIXTIAT compatible evaluation board ACSO04 sec lasi page of this data sheet for description Throughput Rate in calculated by the formola minimum conversions second IBM POXTIAT is a trademark of Imernations Business Machines Corp POWER REQUIREMENTS Vyand Vy v Vp v Supply Current Drein 215V m 5V mA OUTLINE DIMENSIONS Dimensions shown in inches and mm 055 114 01 0 020 0 025 MaK 40 059 00 0 140 43 6 DUN SQUARE LEADS 0 018 t 0001 0 46 a 6 63 1 24 31 4 MAX p 9 sa F a a tet 14 0 amo 4 PLACES BOTTOM VEW WARNING Oe ESD SENSITIVE DEVICE CAUTION OBSERVE PROPER PLUG IN POLARITY TO PREVENT DAMAGE TO CONVERTER PIN DESCRIPTIONS
13. O O AD11709 O O ANALOG High Resolution Programmable DEVICES Integrating A D Converter FEATURES FUNCTIONAL BLOCK DIAGRAM Low Nonlinearity integral 0 001 Differential 0 00035 Microcomputer Based Design Programmable integration Time 1 to 350ms with Resolution from 7 to 18 Bits Programmable Output Data Format Auto Zeroed Operation and Electronic Calibration No External Trim Potentiometers Microprocessor Compatible Interface High Throughput Over 50 Conversions Second for Line Cycle integration Period High Normal Mode Rejection 54dB at 60Hz Smali Size 1 24 x 2 6 x 0 55 max APPLICATIONS Data Acquisition Systems Scientific Instruments Medical instruments Weighing Systems Automatic Test Equipment GENERAL DESCRIPTION The AD1170 is a high resolution integrating A D converter intended for applications requiring high sccuracy and high throughput at low cost A novel conversion architecture provides the user with outstanding accuracy stability and case of use The AD1170 is a complete microcomputer besed measurement subsystem composed of three major elements a highly precise charge balancing converter a single chip microcomputer and a The ADI170 architecture provides for user programmable custom CMOS controller chip The AD1170 offers independently deta format independent of the integration time All data is programmable integration time from one millisecond to 350 computed to 22 bit resolution and the user may spe
14. SCRIPTION MIN TYP MAX UNITS ton Pulse Width 0 19 20 us tom Chip Select to WA Low ne tos Chip Select Hold Time d ns tas Address Setup Time 10 ns tan Address Hold Time 0 ns tos Data Setup Time Lad ns tony Data Hold Time 20 ne Figure 1 Timing Diagrams and Requirements AD1170 The AD1170 contains no internal trims its span accuracy is factory calibrated by using the ECAL Electronic CALibration feature This feature is a firmware routine which measures an externally applied reference voltage compares it to the internal reference voltage and computes a span correction factor which is stored in nonvolatile memory The correction factor is then applied to all subsequent measurements thereby compensating for the reference error The ECAL function may be invoked by the user at any time thereby replacing the usual trim potentiometer with s totally electronic calibration capability UNDERSTANDING THE AD1170 SPECIFICATIONS The AD1170 because of its unique conversion technique is specified quite differently from more conventional integrating converters The following sections will help the user to understand where the sources of error arc and how to extract the best possible performance from the converter There are two primary sources of error in the AD1170 integral nonlinearity of the charge balancing converter which influences all conversions equally regardless of the integration period and calibration period and the noise err
15. SY signal is high will be ignored BITI The DTA RDY bit also available on Pin 10 of the module goes high to indicate that the data from the most recent conversion is available in the LOW DATA MID DATA and HIGH DATA registers This bit is cleared at the start of the next conversion It may also be cleared by executing an EOI command BIT2 The DATA SAT bit is set by any conversion which is saturated i e any conversion whose output data exceeds positive or negative full scale BIT3 The CMD ERR bit indicates that the most recently loaded command contained a contextual or syntactic error or was not recognized It is cleared when the next command is loaded BIT4 The INT bit also available on Pin 11 of the module goes high to indicate that the input signal is currently being integrated It is used in multiplexed systems to determine when the input multiplexer may be switched BITS The PWRUP bit also available on Pin 14 of the module goes high when the module is powered up or when the RST command is executed It remains high until device initialization is complete This signal is used to indicate readiness of the converter after system initialization D DATA DATA UNUSED CONTENTS INDETERMINATE Figure 7 The Status Byte OUTPUT DATA FORMAT The AD1170 architecture allows a programmable data format independent of the integration time The user may specify any resolution from 7 to 22 bits and may specify either offset bina
16. This configuration yields very high CMR enhanced by the 1B31 low pass filter and the integrating conversion scheme of the AD1170 In addition fixed offsets caused by bridge imbalance can be nulled out by the AD1170 with a power up initialization command from the microcomputer see COMPENSATION OF EXTER NAL OFFSETS section The full scale output of the 1B31 and Transducer can also be normalized to AD 170 full scale through the electronic calibration command ECAL Both the offset and full scale correction data can then be stored in nonvolatile memory to eliminate repeating this trim process after each power up The AD1170 eliminates a potentiometer or software overhead which might otherwise be needed for these functions NOTES o ImVI LOAD CELL SVEXCITATION 18env FS GAIN KD USE 1oparn C GAP RESISTOR FOR LOW GAIN TEMPCO Figure 14 Pressure Transducer Data Acquisition Using 1831 and AD1170 AC5004 an IBM PC XT AT Compatible Evaluation Board for the AD1170 FEATURES Compatible to the IBM PC XT AT or Equivalent Menu Driven Demonstration Software Input Mating Connector Full Documentation Example Listings of BASIC Programs Schematic Assembly Drawing Complete Set of Tools to Evaluate an AD1170 A D Converter GENERAL DESCRIPTION The ACS004 was designed as a support too to enable the user to casily and quickly evaluate Analog Devices AD1170 high resolution programmable integrating A D converter The AD1
17. bined effect tends to asymptotically approach a baseline value determined by the shorter of the two For example a T cal greater than 10 milliseconds docs little or nothing to improve the noise performance for conversions using a T int of 1 millisecond Table Conversion of Noise Error to DNL and Usable Resolution SIGNAL INPUT CONNECTIONS The AD1170 has both a positive input pin IN as well as a negative input pin IN but the AD1170 input is not a true differential input The negative input pin is an input used during calibration cycles to establish the zero reference In applications with static ground offsets the IN pin may be used as a ground sense input to sense a signal reference point which is offset from analog common by a small differential Both the IN and IN signals must have a bias current path back to analog com mon Figure 5 illustrates the proper use of the input signal connections Figure 5 input Power Reset and Clock Connections REV A oe RESET A reset sequence must be accomplished after power up and before any access to the converter The RESET line initializes the internal logic of the AD1170 This line may be driven from an external source such as may exist in most computer based systems or it may be connected to a simple RC circuit which will automatically invoke a reset sequence at power up Figure 5 illustrates the recommended circuit When driving the RESET line from an exte
18. ce voltage must be presented to the input before this command is executed and the input must remain stable until the end of command execution is signaled by the BUSY line or the BUSY bit in the status word The calibration data computed by this command is applied to all subsequent conversions but is not made nonvolatile until a SAVA command is performed Tint Ims 250ps o 250us Figure 11 Synopsis of Commands AD1170 EOI 10001000 EO End Of Interrupt clears the DTA RDY bit in the status byte as well as the DTA RDY line Pin 10 It is provided as a means of clearing the interrupt source in systems which use an interrupt upon data ready ELS 00100000 ELS External Line Sampie measures the period of the logic signal applied to the ELS input Pin 12 This period is loaded into the register associated with the last entry of the table in Figure 10 Input conversions using this measurement as the integration period may be performed by invoking a CNVP command or by setting the default integration period with the SDI command This command is intended for use in environments with varying line power frequency periodically invoking this command allows effective tracking for improved normal mode EIS 00101000 EIS External Integration Set is used to establish an arbitrary integration period from 1 millisecond to 350 milliseconds To use this command first load the PARAMETER 1 and PARAM ETER 2 registers with the 16 bit b
19. cify any milliseconds and data format offset binary or two s complement _rexolution from 7 to 22 bits Usable resolution will typically from 7 to 22 bits The converter is fully auto zeroed and exhibits be limited to 18 bits due to measurement and calibration LEAVE NC PINS UNCONNECTED N a span drift of only 9ppm C assuring stable accurate readings noise error The AD1170 may be interfaced to any microcomputer based 3 Electronic digital calibration eliminates the need for trim system in a memory mapped or T O mapped fashion via an 8 bit potentiometers Calibration can be performed at any time by data bus The AD1170 s advanced features are controlled by applying an external reference voltage to the input and invoking simple commands sent to it vis this bus a calibration command The calibration data is stored in an The converter utilizes surface mount technology and is housed internal nonvolatile memory chip in a small 1 24 x 2 5 x 0 55 package It operates from 15V de 4 Internal calibration cycles may be programmed to occur and SV dc power whenever the converter is idle assuring negligible offset drift PROD HTS and only 9ppm C span drift 1 The AD1170 unlike dua slope converters offers the user 5 The conversion rate is greater than 50 conversions per second the capability of programming the integration time by selecting when programmed for 60Hz line cycle integration The one of seven preset integrati
20. converters is a function of the integration time long conversions result in very high resolution while short conversions provide lower resolution In the AD1170 all internal computations are always carried out to 22 bit resolution but useable resolution is limited by the peak to peak noise as determined by T cal and T int The chart shown in Figure 4 illustrates the typical peak to peak poise in ppm Span versus T int and T cal These numbers can be used to indicate how much useable resolution can be 6 VOLTS CAL DISABLED UNITS T int Ims najn n2 m 10 ppmof SPAN toms YZ mfn ja 2 zoms a a woms ZAA we Ao 166 7ms VIO LLL fo Figure 4 Typical Peak to Peak Noise in ppm Span Versus T int and Tical 4 expected under a given set of operating conditions For example a peak to peak noise of 8ppm is approximately analogous to a flicker of 0 5LSB at 16 bits of resolution Under these conditions a user could set the default format for the AD1170 to 16 bit resolution and abserve no more than 1 2LSB of differential error See Table I for conversion of typical peak to peak noise to Differential Nonlinearity and Useable Resolution The chart in Figure 4 may also be used to determine the minimum effective calibration time for a specified integration period the noise contributions of both the measurement cycle and the calibration cycle combine as the root sum square and the com
21. e error equally across the whole span of the converter it is possible to intentionally introduce a span error during the ECAL procedure as shown in Figure 3 This scheme sacrifices positive full scale accuracy in order to minimize negative full scale error The oct result is a relative sccuscy equal to the integral nonlinearity ERROA t VOLTS INTENTIONAL MISCALIBRATION CQUALIZES KAROR AT BOTH ENOS OF SCALE Figure 3 Relative Accuracy with Intentional Span Error at F S In both cases the accuracy of the input offset which is servo controlled is not compromised MEASUREMENT CALIBRATION NOISE Measurement noise refers to the conversion to conversion uncer tainty caused either by mathematical truncation or device noise Calibration noise is actually the measurement noise resulting from the calibration process The converter stabilizes itself by performing internal measurements of the reference and of ground these measurements have the same uncertainty due to noise as does the normal measurement process The measurement and calibration noise error of the AD1170 determines the differential linearity or useable resolution of the converter This parameter determines the usable resolution because it defines what codes can be seen through the noise The specified value is the amount of error in either direction from the average reading which will not be exceeded for 95 of all conversions This parameter as in ail integrating
22. ient to random access memory The user is cautioned that the nonvolatile memory used in the AD1170 has a finite endurance of 1000 write cycles minimum Assuming that the AD1170 is calibrated weekly this implies a device life span of greater than 19 years Less frequent calibrations mean a proportionately longer life span This means ECAL may be performed any number of times but the user should limit the number of SAVA commands in order to extend the life span of the nonvolatile memory Since the SAVA command saves all nonvolatile parameters the user should be sure that the other default parameters such as integration time and data format are set to their desired values before SAVA is invoked 8 REV A NONVOLATILE MEMORY The internal nonvolatile memory in the AD1170 is used to store the various nonvolatile parameters associated with A D operation for example the integration period data format ECAL cocffi cient etc In addition eight 16 bit words of the nonvolatile memory are made available to the user for general purpose use They may be accessed using the RDNV and WRNV commands Because the nonvolatile memory is specified for a finite endurance of 1000 write cycles minimum it is best used for data which docs not regularly need to change such as configuration information or system calibration parameters FACTORY DEFAULT SETTINGS The AD1170 is calibrated at the factory the factory default ings are Format 16 b
23. inary number N which is calculated using the following expression N 2 T inty21 333E 6 After the iow and high bytes representing N are loaded into the PARAMETER and PARAMETER 2 registers respectively execute the EIS command Once this command is executed the externally loaded integration time can be used via the CNVP or SDI commands RESA 01101000 RESA REStore All restores all configuration parameters default integration time default calibration time data format EIS ELS period NULL value and electronic calibration dats from non volatile memory After executing this function all parameters will be restored to their last value as saved by the SAVA com mand SAVA 01001000 SAVA SAVe All saves all programmable attributes default integration time default calibration time dats format EIS ELS period NULL value and electronic calibration data into non volatile memory SDI 00111C C Cy SDI Set Default Integration time sets the default integration time to one of the eight preset times listed in Figure 10 The three bit code for the desired integration time is embedded in the lowest three bits of the command code SDF 00110000 SDF Set Default Format sets the default data format according to the five bit code loaded into the PARAMETER 1 register prior to execution of this command The table in Figure 8 illustrates the construction of the five bit code according to the desired data format and resolution SCAL 11000000
24. it offeet binary Default T int 16 667 milliseconds code 2 Default T cal 100 milliseconds code 4 THE AD1170 COMMAND SET The AD1170 command code set includes 20 different functions Some of the commands require no parameters while others require one or two parameters which must be loaded into the PARAMETER 1 and PARAMETER 2 registers prior to loading the command register Some commands for example CNVP have their option parameter embedded in the lowest three bits of the command itself The execution time for any command depends on the command Figure 11 is a synopsis of the available commands as well as estimates of their execution ames Each of the commands described below is preceded by an opcode name along with the digital code in binary ECAL ilasaslil CALEN Enable Background Calibration CALDt Disable Background Catibration EXECUTION TIME FUNCTIONAL DESCRIPTION APPROX Pertorm a Single Conversion Using the Default Integration Time Pertorm a Single Conversion Using the Specified integration Time Flint 3ms is Measure Period of Signal atthe ELS input 2x Tint 20ms Pertorm Electronic CALbration Routine S seconds eee es Set Default Calibration Period 2 Tae Ons RestoreAliNonvolatileParameterstromMemory 2 3me_ _ Save AlNonvolatleParameterstoMemory 150m Write a Word to the User EEPROM Ares 22ms Read a Word from the User EEPROM Area CleartheDataReedyFag
25. ition to the command byte they must be written into the second and third parameter bytes of the image before writing the command byte This is because writing the command byte triggers the microprocessor to begin command interpretation Following the execution phase of any command the CMD ERR bit in the STATUS byte will indicate acceptance or rejection of the command When set this bit indicates that there was a contextual or syntactic error in the command or parameters Conversions may be initiated either by bus command or by a high to low transition of the EXT CC tine Externally triggered conversions behave in the same way as bus triggered conversions except that the BUSY line and the BUSY bit in the status word remain inactive the end of execution of externally triggered conversions must be determined by examination of the DTA RDY line or the DTA RDY bit in the STATUS word THE STATUS BYTE The lowest readable byte of the device image is the STATUS byte it contains six bits of information about the current status of the AD1170 This byte may be examined by the host processor at any time The individual bits in the status byte see Figure 7 are assigned the following functions BITO The BUSY bit is an inverted version of the signal on Pin 7 of the module When low it indicates that the AD1170 is ready to receive a command When high it indicates that the AD1170 is busy executing the last command Any commands loaded while the BU
26. lating a tri stated condition on the bus to insure that neither RD or WR are selected INIT SETB P DISABLE RD SETB P1 3 AND WR MOV P2 OFFH SET P2 TOALL ONES To write 2 command to the AD1170 first set the state of the P1 1 and P1 0 lines for the address corresponding to the byte to be written to Set the P2 port to the command data then strobe the WR line by first clearing the P1 3 line and then setting it WRCMD CLR P1 0 FIRST CLEAR AOAND At CLR Pi TO POINT TOCMD BYTE MOV P2 CNV CNV IS THEOPCODE FOR 3A SINGLE CONVERSION CLR P3 STROBE THE WR LINE SETB P1 3 ONE TIME MOV P2 OFFH CLEAR DATA BUSTO ALL ONES To read a byte from the AD1170 first set the P1 0 and P1 1 lines to point to the address of the byte desired Bring the RD line low reading the contents of P2 Return the RD line high RDSTAT CLR P10 POINT TO STATUS BYTE CLR PII CLR P12 BRING RD LINE LOW MOV A P2 sREADCONTENTS OF BUS SETB P1 2 sRESTORE RD LINE HIGH AD1170 PRESSURE TRANSDUCER DATA ACQUISITION A two module solution for microcomputer based data acquisition uses a 1B31 hybrid signal conditioner and an AD1170 as shown in Figure 14 A 3 millivoly volt pressure transducer c g Dynisco s 800 series is interfaced to a model 1B31 configured for a gain of 333 3 to provide a 0 to 5 volt output The regulated excitation voltage is 5 volts and is used as the reference input for the AD1170 to produce ratiometric operation
27. nabled and NULL will be disabled NULL 01110000 NULL measures the input signal using the curent integration time value and stores the measurement in internal RAM It allows the user to establish the value of offset voltage at the input and subtract that offset from subsequent conversions through the execution of the NULEN command The user must insure that the sum of the offset value plus the full scale input is less than the 6 volts linear input range of the AD1170 Ideally the offset value to be nulled should be no more than a few hundred millivolts in amplitude The value mcasured by the NULL command is saved and restored by the SAVA and RESA commands maintaining this value through subsequent powerups The NULL command need only be invoked when a new null measurement is desired NULEN 01111000 NULEN NULI ENabk subtracts the value measured and stored by the last NULL command from all subsequent con versions When NULEN is in effect each conversion s length will be extended by approximately 700 microseconds NULDI 10000000 NULDI NULI Disable cancels the effect of the NULEN command This logic signal should be a TTL or CMOS compatible continuous waveform It need not be symmerrical but the HIGH or LOW time should not be less than 25 microseconds REV A Applying the AD1170 IBM PC INTERFACE Figure 12 is an example of an AD1I70 1BM interface suitable for the IBM PC or XT personal computers In this case the
28. om mand s effect The sum of the offsct value plus the full scale input should bc less than the 6 volts linear input range of the AD1170 The offset value to be nulled should ideally be no more than a few hundred millivolts in amplitude The NULL command does not need to be executed every time the AD1170 is powered up Since the value measured by the NULL command is saved and restored by the SAVA and RESA commands the value of the null will be the one saved during the last SAVA command Execute a NULL command only when a new null measurement is desired When NULEN is in effect the length of each conversion will be extended by approximately 700 microseconds ELECTRONIC CALIBRATION The AD1170 contains an Electronic CALibration capability which along with the internal nonvolatile memory chip effectively eliminates the need for trim potentiometers of any kind This capability abbreviated as ECAL should not be confused with the internal background calibration cycles ECAL is a completely distinct function used to calibrate the AD1170 to an external reference standard The ECAL function measures the ratio of the internal reference voltage in the module with respect to an externally applied reference voltage The resulting coefficient is applied to the math computations for all subsequent conversions effectively compensating the module for absolute valuc errors in its own reference The ratio is stored in random access memory until
29. on periods or by loading an maximum conversion rate is greater than 250 conversions per arbitrary integration period over the interface bus second using a one millisecond integration period REV A Information furnished by Analog Devices is believed to be accurate and reliable However no responsibility is assumed by Analog Devices for its use nor for any infringements of patents or other rights of third parties One Technology Way P O Box 9106 Norwood MA 02062 9106 U S A which may resuit from its use No license is granted by implication or Tel 617 329 4700 Fax 617 326 8703 Twa 710 394 6577 otherwise under any patent or patent rights of Analog Devices Telex 924491 Cable ANALOG NORWOODMASS ADI 1 70 SPECIFICATIONS typical 25 C V 15V Va 5V unless otherwise specified Modet RESOLUTION ACCURACY Integral Noalincari THROUGHPUT RATE Time Integrate ims Time Integrate 16 667ms Time Integrate 00ms DIFFERENTIAL NONLINEARITY Tin T Ims iOm 16 667ms 100ras 300ms J00rns conv S conv S conw POWER SUPPLY REJECTION RATIO Span Error vs Analog Supply Voltage INPUT CHARACTERISTICS Analog Input Range de de Plus Normal Mode Voltage Absolute Maximum Without Demage Normal Mode Rejection G HoHz 50Hz Input Bius Current input Impedance REFERENCE Output Voltage Output Current Input Range DIGITAL LEVELS taputs Low High Outpuss Low 4mA High 100p A WARMUP TI
30. or of the mceasurement cali bration process which is a function of the integration period and calibration period as selected by the user INTEGRAL NONLINEARITY The integral nonlinearity of the charge balancing converter CBC is 10ppm 0 001 of Span This specification is an endpoint vonlinesrity measurement i c the typical deviation seen from s straight line drawn between the CBC output at 5 volts and its ourput at 5 volts This specification excludes any gain or offset gzror If the converter was externally calibrated at its end points 5 volts and 5 volts then the integral nonlinearity would also be the relative accuracy of the converter This is not the case in the AD1170 however because calibration is performed internally at 0 and 5 volts rather than and 5 volts This calibration technique superimposed upon the integral nonlinearity of the CBC results in the curve shown in Figure 2 VOLTS S VOUS INPUT VOLTAGE ee P Figure 2 Relative Accuracy and integral Nonlinearity when Calibrated As shown in the diagram the calibration technique tends to exaggerate the relative error at the negative end of the scale and reduce the error between 0 and 5 volts This characteristic happens to be most beneficial when using the AD1170 in systems where the input comes from a sensor whose signal is mostly positive such as a thermocouple For systems where the user desires to minimize the relativ
31. pw sicnay teenies Address ControlLines e RB ResdData Strobe 5 WA Write Dots Strobe FE Chip Select When Low Indicates Device Busy When High Indicates Device Ready for Command yehen High indicates That Data From Most Recent Conversion Command is Reedy When High Indicates Device is Currently integrating H input Signal Ge Goas Low to indicate Integration i Complete 1 Externeli Uns ne Semp pie input Used with Eis Command o Sense an Externally Provided Saniple of the Line Frequency When High Indicates Power Up Initiclizetion jin Progress 36 38V_ Negative Analog Power Supply ee Analog Power Supply Eia Analog Common the Asterance Point for Analog H Power Supplies H f 19 tt Pasive Signat input 20 IN Negative Signal input 2s jREFOUT internat SY Reference Output a 23 REFIN _ Raterence input Normalty Connecied io Ret Out j a e ae Digits Common tha Reference Point tor the Digita Power Supp 29 EOG _ External Convert Command input Reset Input Usualty Connected to an RC Network of Automatk Reset Upon Power Up XTAL OUT Connectians tor 12MH Crystal Saries Resonant XTALIN 13042 ESR Anernativety Xtal in May Be Driven From en External 12MH2 Logic Signal 33 40 6700 Bidirectional Date Bus 8 9 13 15 22 24 DO NOT CONNECT 28 27 FACTORY DEFAULT SETTINGS The AD1170 s internal nonvolatile memory stores various A D parameters as programmed by the user
32. rnal source the linc must be held high for at least 2 microseconds after the oscillator is running and stable typically 300 microseconds after power is applied in order to assure a proper reset CLOCK The AD1170 requires a 12MHz clock for operation This clock may be supplicd by connecting the XTAL OUT and XTAL IN pins toa 12MHz crystal along with two resistors and two capacitors as shown in Figure 5 The user may also supply a 12MHz logic signal from an external source such as may be available in the user s system In this case the external clock should be applicd to thc XTAL IN pin and the XTAL OUT pin should remain unconnected POWERING THE AD1170 For best performance the user should pay careful attention to proper power supply bypassing as well as grounding Analog common and digital common are not connected internal to the module but must be connected externally Figure 5 illustrates the proper connection of power and ground to the ADI 170 REFERENCE CONNECTIONS The internal 5 volt reference of the AD1170 is brought out to Pin 21 of the module for normal operation it should be connected to the reference input Pin 23 An external reference voltage of from 4 5 to 5 5 volts may be applied to the reference input Pin 23 and the reference output may remain unconnected The data will be ratiometric to that reference The input impedance of the reference input is ap proximatcly 16K ohms The reference input is not dynamic
33. ry coding or two s complement coding Programming the data format is accomplished via the use of the SDF command using the format code described in the table in Figure 8 as the PARAMETER 1 value X DON T CARE C Ce Cs X FORALL DATA FORMATS Figure 8 Format Code It should bc noted that the AD1170 computes all data to 22 bit resolution However not all 22 bits are useabic since the differ ential performance is largely dependent upon factors such as integration period and calibration period The SDF command simply serves to round off the result to the specified number of bits The graph in Figure 4 can be used to estimate the amount of useable resolution achievable for a specified integration period and calibration period The output data is always right justified within the three ourput bytes LOW DATA MID DATA and HIGH DATA If two s complement format is selected the MSB of the data is inverted and cxtended all the way to the top of the HIGH DATA byte For example if 16 bit two s complement format is selected the data will appear in the LOW DATA and MID DATA bytes and the MSB will be 0 for positive inputs The format is a nonvolatile parameter whenever an SAVA command is executed the current format will be saved to nonvolatile memory and will become the default format upon powerup The minimum duaration for EXT CC is one microsecond 2Since the sign is extended al the way to the top of the uppermost byte the
34. s two conversions of 20 milliseconds plus approximately 9 milliseconds for the internal mathematics The user may also disable or enable background calibration In systems where the AD1170 may be periodically idle i c not performing input conversions background calibration is a good choice This mode is enabled with the CALEN command and will cause the AD1170 to continually initiate an internal calibration cycle whenever the converter is otherwise unoccupied Any conversion commands received during a cal cycle will cause that cal cycle to be aborted in favor of the input conversion thereby giving the user priority aver calibration This mode of operation is automatic and transparent The CALDI instruction is used to disable background calibration When this instruction is executed the converter will be completely idle between convert commands and calibration cycles will only occur when invoked by the SCAL command This mode of operation is best when the user would like to perform input conversions at the maximum rate and or when the system affords a specific convenient time to perform calibration There are no hard and fast rules about the best way to apply all of this flexibility but best performance will be obtained if the following points are observed Consult the chart in Figure 4 to determine the minimum effective calibration period for use with a desired integration period Don t use automatic background calibration
35. unless your system will allow the converter enough uninterrupted time to perform at least one calibration cycle For example if you are using a calibration period code of 3 your system must periodically allow at least 49 milliseconds without a convert command or calibration will not occur Remember that the purpose of the calibration cycle is to cancel the intrinsic drift of the charge balancing converter within the AD1170 itself If the converter is in a stable envi ronment calibration may be done less frequently The best possible performance will be achieved in stable ambient tem peratures where calibration is manually invoked by the system at relatively long intervals using the longest allowable calibration ume Very short calibration times although allowed by the AD1170 firmware are not especially useful because they introduce more error than they compensate The only useful purpose of very short calibration times is in systems which are operating in rapidly changing ambient temperatures and then only for relatively low resolution conversions COMPENSATION OF EXTERNAL OFFSETS An electronic null feature compensates for offset errors of signal conditioning stages preceding the AD11 70 The null feature comprises three commands NULL measures the input signal using the current integration timc and stores it in internal RAM NULEN subtracts the measured value from all subsequent conversions NULDI cancels the NULEN c
36. version before resuming rapid scanning The AD1170 offers the user a number of different ways to sct the integration period The simplcst way is by using the SDI command to set the default integration period to one of seven preset periods Ims 10ms 16 66ms 20ms 100ms 166 66ms 300ms The first two preset periods offer fairly rapid scanning at reduced resolution the other five represent American and European line voltage standards or multiples thereof For single conversions without altering the default integration time the CNVP command may be used which also allows the selection of one of these seven preset periods These preset periods and their corresponding codes are listed in the table of Figure 10 Another way in which the integration period may be programmed is via the EIS command which allows the user to load the externally definable period register with a binary value proportional to the desired integration period Using this technique the user may specify any period from one millisecond to 350 milliseconds with 200 microsecond accuracy Access to this user definable period is via the SDI or CNVP commands the last entry in Figure 10 is used to select the period defined by the EIS or ELS command REV A NOTE This code is used for externally loaded integration times defined with the EIS Command or externally measured times from the ELS Command The value can be anywhere from 1 Millisecond to 350 Milliseconds

ANALOG DEVICES AD1170 handbook

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