Advantech PCM-4822, User Manual

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48 PCM-4822 User's Manual
Digital Input and Output Operation
Digital Input and Output are a group of control signals that are
utilized to control external devices requiring ON/OFF circuitry.
The PCM-4822 supports 4-channel digital input and 4-channel
digital output. These digital input and output levels are TTL
compatible.
You can use the I/O read or write command to access the digital
I/O port. An output register has been designed to latch the output
data. However, this cannot be read back for checking purposes.
The following figure shows the design of a proposed circuit when
connected with other TTL devices.
When receiving an OPEN/SHORT input signal from a switch or
relay, you are advised to add a pull-up resistor to your system that
will keep the input signal at a high level setting when the circuit is
set to OPEN.