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You can specify channel settings by writing directly to the MUX scan
register. You use the MUX scan register to point to a specified channel
when you set channel input ranges (with BASE+1). After you set the
input range, you will need to reset the MUX register for the proper
start and stop channels.
You can trigger an A/D conversion from software, the card's on-board
pacer or an external pulse. Bits 1 and 0 of register BASE+9 select the
trigger source.
1. If you select software triggering, a write to the register BASE+0
with any value will trigger an A/D conversion. You would not
normally use software triggering in high speed A/D applications
because the triggering rate is too slow.
2. You can use the PCL-818L's on-board Intel 8254 programmable
interval timer/counter to generate timing related signals. Counters
1 and 2 of the Intel 8254 can provide A/D converter trigger pulses
with precise periods. The 8254 can generate pacer output between
2.5 MHz and 71 minutes per pulse. Chapter 8 covers the details of
the Intel 8254 timer/counter.
Pacer triggering is ideal for interrupt and DMA data transfer,
normally used in A/D applications which require higher conver-
sion speeds.
3. You can provide an external signal to trigger the A/D conversion.
Connect the external signal to TRIG0 (pin 35 on connector CN3).
You would normally use external triggering if your application
requires A/D conversions not periodically, but conditionally, e. g.,
measuring a voltage when a limit switch closes. The A/D conver-
sion starts at the rising edge of the external trigger pulse.
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PCL-818L User's Manual
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