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34 • Operation Theorem
4.5 Digital Input and Output
To program digital I/O operation is fairly straightforward. The digital input
operation is just to read data from the corresponding registers, and the
digital output operation is to write data to the corresponding registers. The
digital I/O registers‘ format is shown in section 3.14. Note that the DIO
data channel can only be read or written in form of 16 bits together. It is
impossible to access individual bit channel.
The PCI-9111 provides 16 digital input and 16 digital output channels
through the connector CN1 and CN2 on board. The digital I/O signal is
fully TTL/DTL compatible. The detailed digital I/O signal specification can
be referred to section 1.3.
Digital Output (DO)
Digital GND (DGND)
Digital Input(DI)
From TTL Signal
To TTL Devices
PCI-9111
Outside Device
74LS244
74LS373
4.6 Timer/Counter Operation
4.6.1 Introduction
One 8254 programmable interval timer/counter chip is installed on
PCI-9111. There are three counters in one 8254 chip and 6 possible
operation modes for each counter. The block diagram of the timer/counter
system is shown in following diagram.
Counter #0
Internal 2 MHz Clock
Timer #1
Internal Timer Pacer
Timer #2
8254 Chip
G
C
G
C
G
O
O
O
'H'
'H'
AD Trigger Signal
Gate Control
Pre-Trigger
Control
Pre-Trigger
Signal
(Pin-12 of CN3)
C
Figure 4.6.1 Timer/Counter System of PCI-9111