Publication 1734-UM002C-EN-P - July 2003
2-22 What is the 1734-ADN(X) Adapter?
Communicating with
I/O Modules
The adapter module supports multiple communication choices. These
choices all use the default I/O structure previously described. The
adapter’s master (e.g., 1756-DNB) makes the actual communication
choice. The choices are:
• Polled – Adapter sends data in response to received data.
• Strobe – Adapter sends data in response to the strobe command.
The single bit allocated to the adapter in the strobe message is
not used. If the configured size of the input data (sent from the
adapter) is greater than 8 bytes, the strobe connection
establishment will fail. In this case, the input size must be
reconfigured to 8 bytes or less (only 6 bytes are I/O data
because the first 2 bytes are the status word).
• Change of State – Adapter sends data based on detection of any
changed value within the input data. Data is independently
received based on change of state from the sender. Data in both
directions can be acknowledged or unacknowledged depending
on the run time configuration of the system.
• Cyclic – Adapter sends data cyclically based on a configured
time value. Data is independently received cyclically from the
sender. Data in both directions can be acknowledged or
unacknowledged depending on the run time configuration of
the system.
The adapter uses these messages to solicit data from or deliver data to
each device. Data received from the devices (i.e., input data) is
organized by the adapter and retransmitted to the master. Data
received from the master (i.e., output data) is organized in the adapter
and sent on to the I/O modules.
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