Series AVME9125 VMEbus 6U Analog Input Board
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Calibration Programming Example 1
Assume that channels 0 to 3 are connected differentially, and
corrected input channel data is desired. The calibration
parameters (Count9.79V and Count0V) remain to be determined
before the gain and offset coefficients can be calculated.
Determination of the Count0V Value
1.
Execute Write of 0420H to Control Register at Base
A 42H.
A.
Select No Interrupt Level
B.
Auto Zero Calibration Voltage
C.
Burst Single Scan Mode
D. Timer
Disabled
E. Interrupts
Disabled
2.
Execute Write of 1F00H to End/Start Channel Value
Register at Base A 48H. This will permit 32
conversions of the Auto Zero value to be stored in the
32 Mail Box Buffers.
3.
Execute Write 0001H to the Start Convert Bit at Base
A 52H. This starts the burst single mode of
conversions. Thirty two conversions of the Auto Zero
are implemented and stored in the 32 Mail Box Buffers.
4.
Execute Read of the 32 Mail Box Buffers at Base
A 60H to 9EH.
5.
Take the average of the 32 ADC values and save this
number as Count0V.
6.
Determination of the Count9.79V Value
7.
Execute Write of 0410H to Control Register at Base
A 42H.
A.
Select No Interrupt Level
B.
Select 9.79V Calibration Voltage
C.
Burst Single Scan Mode
D. Timer
Disabled
E. Interrupts
Disabled
8.
Writing the Start Channel Value, End Channel Value,
and the Gain Selects is not necessary if they have not
been changed from that programmed in steps above.
9.
Execute Write 0001H to the Start Convert Bit at Base
A 48H. This starts the burst single mode of
conversions. Thirty two conversions of the 9.79 volt
calibration voltage are implemented and stored in the 32
Mail Box Buffers.
10.
Execute Read of the 32 Mail Box Buffers at Base
A 60H to 9EH.
11.
Take the average of the 32 ADC values and save this
number as Count9.79V.
12.
Calculate Gain and Offset Coefficients and Write to
Corresponding Registers
13.
Since all parameters are known, the gain and offset
coefficients can be determined.
A.
The offset coefficient is the average of the 32
Count0V values measured. An example,
illustrating how the offset coefficient value is
determined, is given in the Offset Coefficient
Register section.
B.
The gain coefficient can be calculated using
the averaged Count9.79V and Count0V
values as shown in equation 3. The
procedure for determining the coefficient,
down to 1/4 bit resolution, is given in the Gain
Coefficient Register section.
14.
Execute Write of the least significant word of the Gain
Coefficient to board register at Base A 58H.
15.
Execute Write of the most significant word of the Gain
Coefficient to board register at Base A 56H.
16.
Execute Write of the Offset Coefficient to board register
at Base A 54H.
17.
Measure Channels 0 to 3
18.
Execute Write of 0400H to Control Register at Base
A 42H.
A.
Select No Interrupt Level
B.
Burst Single Scan Mode
C. Timer
Disabled
D. Interrupts
Disabled
19.
Execute Write of 0300H to End/Start Channel Value
Register at Base A 48H. This will permit
conversions of channels 0 to 3.
20.
Execute Write 0001H to the Start Convert Bit at Base
A 52H. This starts the burst single mode of
conversions. Conversions of channels 0 to 3 are
implemented and corresponding results are stored in the
first four Mail Box Buffer locations at Base A
60H to 66H.
21.
Execute Read of the 4 Mail Box Buffers at Base Address
+ 60H to 66H. The data represents the desired,
corrected value.
22.
If channel response time requirements are not high
speed it is recommended that a running average (i.e. of
the last 8, 16, 32, etc.) of readings be maintained for
each channel. This will minimize noise effects and
provide the best accuracy.
GENERATING INTERRUPTS
The AVME9125 board initiates interrupts and uses the
Interrupt Level data of the Control register to map the request to
the desired VMEbus interrupt level. The board then waits for an
interrupt acknowledge from the VMEbus host after asserting the
appropriate VMEbus interrupt request.
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