Rockwell Automation Allen-Bradley 1769-ASCII, User Manual

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Rockwell Automation Publication 1769-UM012B-EN-P - January 2014 71
Chapter
3
I/O Memory Mapping
When both serial channels are active, you can alternate between receiving data in
the buffer from both ports simultaneously or one at a time.
ASCII Module Behavior when
not in Run Mode
The 1769-ASCII module transmits data out the serial port when the controller is
only in Run mode. It sends data once the Tx Transaction ID changes after the
controller transitions into Run mode.
The 1769-ASCII module delivers data received on the serial ports to the
controller even when it is not in Run mode. When not in Run mode, the module
acts as if Master Handshaking is not enabled. Therefore, new data is placed in the
input tag and the Rx Transaction ID increments. When it receives new serial data
after the transition to Run mode, the module follows whatever rules are
configured then. In your program, use the Rx Transaction ID value in the input
tag on the first scan to compare for new data.