Timing I/O Circuitry; Figure 3-5. Timing I/O Circuitry Block Diagram - National Instruments PC-LPM-16/PnP User Manual

Timing I/O Circuitry

National Instruments Corporation
The PC-LPM-16PnP uses an MSM82C53 Counter/Timer integrated
circuit for data acquisition timing and for general-purpose timing I/O
functions. Three counters on the circuit are available for general use,
but the board can use only one of them, counter 0, internally for data
acquisition timing. Figure 3-5 shows a block diagram of both groups of
timing I/O circuitry.
CTR RD/WR
1 MHz
Clock
8
/
Data

Figure 3-5. Timing I/O Circuitry Block Diagram

The MSM82C53 contains three independent 16-bit counter/timers and
one 8-bit Mode Register. As shown in Figure 3-5, you can use counter 0
for data acquisition timing, and counters 1 and 2 are free for general use.
You can program all three counter/timers to operate in several useful
timing modes. The programming and operation of the MSM82C53 is
presented in detail both in Appendix B, MSM82C53 Data Sheet, and
Appendix D, Register-Level Programming.
The timebase for counter 0 uses a 1 MHz clock generated from an
onboard oscillator. You must externally supply the timebases for
counters 1 and 2 through the 50-pin I/O connector. Figure 3-6 diagrams
the 16-bit counters in the MSM82C53.
A/D Conversion Logic
OUT0
GA TE0
CLK0
CLK1
GA TE1
OUT1
CLK2
GA TE2
OUT2
MSM82C53
Counter/Timer
3-9
Chapter 3 Theory of Operation
OUT0
GA TE0
CLK1
GA TE1
OUT1
OUT1*
CLK2
GA TE2
OUT2
Plug and Play
Interrupt
Interface
PC-LPM-16/PnP User Manual