Diamond Power Products MM-48-AT user manual Autocalibration Operation, Reference Voltages

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12. AUTOCALIBRATION OPERATION

Diamond-MM-48-AT includes a sophisticated autocalibration circuit that manages the calibration of both the A/D and the D/A circuitry. Operation is as follows.

12.1 Reference Voltages

The board contains a precision reference voltage chip that is selected for high stability over time and temperature. The value of the voltage output from this chip is measured at the factory. The board also contains some precision resistor divider ladders that produce intermediate voltages derived from the original reference. All these voltages are measured at the factory and their values are stored in an EEPROM on the board.

12.2 A/D calibration

When the A/D is calibrated, it measures the reference voltages using an extra input multiplexor reserved for autocalibration. The calibration software compares the actual measurements to the stored values and makes adjustments to the board to bring the measurements into tolerance (less than 2 LSBs max, in most cases less than 1 LSB). The adjustments are produced by controlling several 8-bit DACs that are inserted at various points in the circuit. The data written to these DACs is then stored in the EEPROM.

12.3 D/A Calibration

When the D/A is calibrated, the board performs a similar operation. The output of DAC 0 is routed through the calibration multiplexor. The offsets of the other DACs relative to DAC 0 are measured at the factory and stored in the EEPROM. During calibration the average offset is added to the measured output of DAC 0, and this value is used as the comparison value to minimize overall errors.

12.4 Universal Driver Software Support

Calibration is simple when using the Diamond Systems Universal Driver software. Several functions are provided to manage the entire operation, and a demo program is included. For application developers targeting an operating system not supported by Universal Driver, the source code is included so you can incorporate it into your own program.

With the Universal Driver software, you have the option of recalling calibration values each time you change the input range, or leaving the current ones in place. Leaving the current ones in place will match the performance of other A/D boards which also use only a single set of calibration values. Recalling the values specific to the new input range will improve performance by a few LSBs but will result in a time delay since the data must be recalled from the EEPROM and loaded into the DACs.

A/D and D/A maybe calibrated separately. Calibration takes a few seconds and may be performed as often as desired, for example at system startup, once a day, etc.

NOTE: When calibrating the D/A channels, the output voltage of DAC0 will fluctuate between

–full scale and + full-scale as part of the procedure. Any circuitry connected to the DAC during this time may be affected and produce unwanted results.

Diamond-MM-48-AT User Manual V1.01

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Contents DIAMOND-MM-48-AT Table of Contents Description DIAMOND-MM-48-AT Board Drawing Signal Name Definition O Header Pinout and PIN DescriptionJ3 Analog and Digital I/O Signal Name Definition Relay output contacts J4 Relays and OptocouplersOptoisolated input contacts Board Configuration Base AddressBase Address Jumper Position Hex Decimal Interrupt Level SelectionOptocoupler Polarity ReservedAnalog Input Range Overview Base + Write Function Read FunctionLSB MSB Register Map Bit Assignments Write operationsDA7 DA6 DA5 DA4 DA3 DA2 DA1 DA0 Read operationsRegister Definitions Base + WriteDefinitions Base + ReadAD9 AD8 Base + Read/Write A/D Channel RegisterHIGH3 HIGH2 HIGH1 HIGH0 LOW3 LOW2 LOW1 LOW0 Base + Read/Write Digital I/O Configuration Register Base + Read/Write Relay Control PortRELAY7 RELAY6 RELAY5 RELAY4 RELAY3 RELAY2 RELAY1 RELAY0 DIR3 DIR2 DIR1 DIR0DIO3 DIO2 DIO1 DIO0 Base + Read Digital I/O Data and Edge StatusDEDGE3 DEDGE2 DEDGE1 DEDGE0 DIO3 DIO2 DIO1 DIO0 OEN3 OEN2 OEN1 OEN0 POL3 POL2 POL1 POL0Base + Write Channel and Control Register Daupdt DACH2 DACH1 DACH0OEDGE3 OEDGE2 OEDGE1 OEDGE0 OPTO3 OPTO2 OPTO1 OPTO0 Base + Write Command Register Dapre Daprld Reset Fiforst AdstartBase + Read Status Register POL ADCH3 ADCH2 ADCH1 ADCH0Base + Write Configuration Register CKSEL1 CKFRQ1 CKFRQ0 Scnint Clken ClkselBase + Read Configuration & Status Register Adbusy Dabusy CKSEL1 CKFRQ1 CKFRQ0 Scnint Clken ClkselBase + Write Fifo Control Register Fifoth Fifoen ScanenBase + Read Fifo Status Register OVF Fifoth Fifoen ScanenBase + Write Interrupt Control Register Clrt Clrd Clro Clra Tinte Dinte Ointe AinteBase + Read Interrupt Status Register Tint Dint Oint Aint Tinte Dinte Ointe AinteBase + Read/Write Counter/Timer D7 Base + Read/Write Counter/Timer D15Base + Read/Write Counter/Timer D23 Base + Write Counter/Timer Control Register Ctrno Latch Gtdis Gten Ctdis Cten Load CLRCtrno Base + Read/Write Eeprom / TrimDAC Data Register Base + Read/Write Eeprom / TrimDAC Address RegisterBase + Write Eeprom Access Key Register Base + Write Calibration Control RegisterBase + Read Calibration Status Register Base + Read Fpga Revision CodeAnalog Input Ranges and Resolution ResolutionInput Ranges Single Ended and Differential InputsPerforming AN A/D Conversion Trigger an A/D conversion on the current channel LSB = readbase MSB = readbase+1 Data = MSB * 256 + LSBInput voltage = A/D value / 32768 * Full-scale voltage D SCAN, FIFO, and Interrupt Operation TriggerClken Clksel Conversion or ScanFifo Operation Interrupt OperationFifoen Fifoth Scanen Fifoen =Guidelines for Selecting Fifo Use Fifoen and Fifoth Operation TableAinte Fifoen Scanen Analog Output Overview Generating AN Analog Output Autocalibration Operation Reference Voltages12.2 A/D calibration 12.3 D/A CalibrationDigital I/O Operation Procedure for enabling interrupts on selected edges Optocoupler OperationEdge detection assumes OENn = 1 to enable edge detection Polarity and logic readbackRelay Operation COUNTER/TIMER Operation Counter 0 A/D Sample ControlCounter 1 Counting/Totalizing Functions Command Sequences CounterCounter Outpbase+15,0x01 Outpbase+15,0x81 Specifications AutocalibrationGeneral
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