4 4
PCM-3718H/3718HG User's Manual
OUT
CLK IN
CLK IN
OUT
COUNTER 1
COUNTER 2
1MHZ
OR
10MHZ
OSC.
PACER
7.1 The Intel 8254
The PCM-3718H/3718HG uses the Intel 8254 programmable interval
timer/counter version 2. The popular 8254 offers three independent
16-bit down counters. Each counter has a clock input, control gate
and an output. You can program each counter for maximum count
values from 2 to 65535.
Version 2 of the 8254 has a maximum input clock frequency of 10
MHz. The PCM-3718H/3718HG provides 1 MHz and 10 MHz input
frequencies to the 8254 from an on-board crystal oscillator. Jumper
JP1 controls the input frequency. See page 12 for more information.
Counters 1 and 2 on the 8254 are cascaded and operated in a fixed
divider configuration. Counter 1 input is connected to the 1 MHz or
10 MHz clock frequency, and the output of Counter 1 is connected to
the input of Counter 2. The output of Counter 2 is internally config-
ured to provide trigger pulses to the A/D converter, as shown below:
The Intel 8254 has six operational modes, from Mode 0 through
Mode 5. To generate a pacer clock, program both Counter 1 and
Counter 2 for Mode 3 (square wave generation).
Note!: Counter 0 is reserved for future development.
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Страница 5: ...1 General Information CHAPT ER ...
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Страница 21: ...3 Signal Connections CHAPT ER ...
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Страница 27: ...4 Register Structure and Format CHAPT ER ...
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Страница 39: ...5 A D Conversion CHAPT ER ...
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Страница 47: ...7 Programmable Pacer CHAPT ER ...
Страница 57: ...8 Direct Memory Access Operation CHAPT ER ...
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Страница 61: ...9 Calibration CHAPT ER ...
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Страница 65: ...A A P P E N D I X Software Driver User Note ...