National Instruments PC-LPM-16/PnP 사용자 설명서

Appendix D     Register-Level Programming

PC-LPM-16/PnP User Manual

D-30



 National Instruments Corporation

Write to the A/D Clear Register to clear the analog input circuitry, 
which leaves the analog input circuitry in the following state:

•

Analog input error flag OVERFLOW is cleared.

•

Pending interrupt requests are cleared.

To empty the A/D FIFO before starting any A/D conversions, perform 
two 8-bit reads on the A/D FIFO Registers and ignore the data read. 
This operation guarantees that the A/D conversion results read from the 
A/D FIFO are from the initiated conversions rather than leftover results 
from previous conversions.

To clear the analog input circuitry and the A/D FIFO:

•

Write 0 to the A/D Clear Register (8-bit write).

This manual refers to a sequence of timed A/D conversions as a data 
acquisition operation. Counter 0 of the MSM82C53 is used as the 
sample-interval counter. In a data acquisition operation, counter 0 
continuously generates the conversion pulses. The software keeps track 
of the number of conversions that have occurred and turns off counter 0 

Table D-3.     Bipolar Input Mode A/D Conversion Values 

-5.0

-4,096

F000

-2,048

F800

-2.5

-2,048

F800

-1,024

FC00

0

0

0000

0

0000

2.5

2,048

0800

1,024

0400

4.9976

4,095

0FFF

2,047

07FF

a.Book : l.Appendix D  Page 30  Wednesday, November 20, 1996  6:36 PM