Rockwell Automation Allen-Bradley 1769-ASCII, User Manual

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Rockwell Automation Publication 1769-UM012B-EN-P - January 2014 85
I/O Memory Mapping Chapter 3
How to Receive Serial Data
from the 1769-ASCII Module The Produce buffer can include one channel's data or combine both channel's
data in one buffer from the 1769-ASCII module to the CompactBus Master. If
you configure the module to return only one channel's data in the Produce buffer,
the channel can return up to 200-bytes of ASCII data.
A CN0 bit in the Consume buffer is allocated to determine which channel’s
ASCII data the CompactBus Master is actively requesting.
If the 1769-ASCII module is configured to return both channels’ data, the
Produce buffer returns two ASCII buffers each proceeded by its associated 8-byte
header. Under this configuration, the combined length of both channels’ data
cannot exceed the module’s 200-byte ASCII buffer limit.
The ASCII data is updated when the delimiter is received, the buffer completely
fills, or when a time-out event occurs. Every time the buffer is updated, for
example, the Transaction ID is increments when the delimiter receives an
overflow condition. The data is valid only up to the received delimiter in your
memory map. The status byte represents information regarding the ASCII data
record received from the ASCII device and handshaking and buffer status flags.
Master/Slave Handshake The 1769-ASCII module supports a firmware handshaking protocol to prohibit
the module from overwriting input data before the CompactBus Master reads it.
If this mode is enabled, the 1769-ASCII module does not overwrite existing data
in its receive buffer.
Value Meaning
0 Set New Data Status bit and wait for application to increment record number
1 Automatically increment the record number and show the new data when an end event is received