Rockwell Automation Allen-Bradley 1769-ASCII, User Manual

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82 Rockwell Automation Publication 1769-UM012B-EN-P - January 2014
Chapter 3 I/O Memory Mapping
Set Up the Transmit Character Buffer Length
The Transmit Character Buffer Length parameter is the number of characters
that the 1769-ASCII module can receive in its transmit buffer from the
CompactBus Master. This size value determines the maximum size of the
command data sent to the 1769-ASCII module from the Master, that is the
1769-ASCII module Consume Size.
The Consume buffer can include the following:
•
A single channel’s data from the 1769-ASCII module to the CompactBus
Master.
The channel can return up to 200 bytes of ASCII data.
•
Both channels’ data in one buffer from the 1769-ASCII module to the
CompactBus Master (Simultaneous mode)
The Consume buffer returns two ASCII buffers, each proceeded by its
associated 4-byte header. The combined length of both channels’ data
cannot exceed the module’s 200-byte ASCII buffer limit.
Valid settings for the Transmit Character Buffer Length parameter are 0-200. If 0
is selected, the serial port for data is deactivated. Any information in the output
file is ignored.
If the total size of the two channels is greater than 200 characters, the Alternate
mode must be used.
Receive Data Padding
The 1769-ASCII module uses padding to add extra characters to the end of its
receive data string (after the delimiter character). The 1769-ASCII module add
this padding before sending the string to the CompactBus Master as an I/O
response.
This padding allows for the CompactBus Master to always receive a data string
with a constant length. This length is equal to the one specified in the Receive
Character Length parameter.
You specify the Pad mode character to add to the received serial data, which is
0…127 in 7-bit mode and 0…255 in 8-bit mode.