National Instruments AT-MIO-16D, Руководство пользователя

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Chapter 3 Theory of Operation
© National Instruments Corporation 3-13 AT-MIO-16D User Manual
pulse on this output pin. EXTSTROBE* is not necessarily part of the digital I/O circuitry but is
shown here because it can be used to latch digital output from the AT-MIO-16D into an external
device.
Timing I/O Circuitry
The AT-MIO-16D uses an Am9513A Counter/Timer for data acquisition timing and for general-
purpose timing I/O functions. An onboard oscillator is used to generate the 10-MHz clock.
FigureÊ3-6 shows a block diagram of the timing I/O circuitry.
GATE4
RTSI Bus
/
2
/
16
1-MHz CLK
DATA<15..0>
Am9513 RD/WR
CONVERT
SCANCLK
MUX CTR CLK
Data
Acquisition
Timing
SOURCE4
SOURCE3
OUT1
OUT3
OUT4
OUT5
GATE3
Am9513
5
Channel
Counter/
Timer
¸
10
GATE5
SOURCE5
OUT5
GATE2
SOURCE2
OUT2
GATE1
SOURCE1
OUT1
FOUT
I/O Connector
STOP TRIG
Flip
Flop
GATE4
PC AT I/O Channel
(10 MHz)
MYCLK
Figure 3-6. Timing I/O Circuitry Block Diagram
The Am9513A contains five independent 16-bit counter/timers, a 4-bit frequency output channel,
and five internally generated timebases. The five counter/timers can be programmed to operate in
several useful timing modes. The programming and operation of the Am9513A is presented in
detail in Appendix E,
Am9513A Data Sheet .
The Am9513A clock input is one-tenth the MYCLK frequency selected by the W5 jumpers. The
factory default for MYCLK is 10 MHz, which generates a 1-MHz clock input to the Am9513A.
The Am9513A uses this clock input to generate five internal timebases. These timebases can be
used as clocks by the counter/timers and by the frequency output channel. When MYCLK is
10 MHz, the five internal timebases normally used for AT-MIO-16D timing functions are 1 MHz,
100ÊkHz, 10 kHz, 1 kHz, and 100 Hz.