APPENDIX D
PCI-1711/1731 User’s Manual
Advantech Co., Ltd.
www.advantech.com
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MODE 4 –Software-Triggered Strobe
After the mode is set, the output will be high. When the count is
loaded, the counter will begin counting. On terminal count, the output
will go low for one input clock period then go high again.
If you reload the count register during counting, the new count will be
loaded on the next CLK pulse. The count will be inhibited while the
GATE input is low.
MODE 5 – Hardware-Triggered Strobe
The counter will start counting after the rising edge of the trigger input
and will go low for one clock period when the terminal count is
reached. The counter is retriggerable.
D.4 Counter Operations
Read/Write Operation
Before you write the initial count to each counter, you must first
specify the read/write operation type, operating mode and counter
type in the control byte and write the control byte to the control
register [BASE + 30(Dec)].
Since the control byte register and all three counter read/write registers
have separate addresses and each control byte specifies the counter it
applies to (by SC1 and SC0), no instructions on the operating se-
quence are required. Any programming sequence following the 82C54
convention is acceptable.
There are three types of counter operation: Read/load LSB, read /load
MSB and read /load LSB followed by MSB. It is important that you
make your read/write operations in pairs and keep track of the byte
order.
Counter Read-back Command
The 82C54 counter read-back command lets you check the count value,
programmed mode and current states of the OUT pin and Null Count
flag of the selected counter(s). You write this command to the control
word register. Format is as shown at the beginning of this section.
The read-back command can latch multiple counter output latches.
Simply set the CNT bit to 0 and select the desired counter(s). This
single command is functionally equivalent to multiple counter latch
commands, one for each counter latched.
