Rockwell Automation Allen-Bradley 1769-ASCII, User Manual

Page: 81 / 118

Rockwell Automation Publication 1769-UM012B-EN-P - January 2014 81
I/O Memory Mapping Chapter 3
Set Up the Transmit Delimiter
The 1769-ASCII module uses the transmit (and exclude) delimiter to determine
the number of bytes to transmit to your ASCII device. The 1769-ASCII module
transmits up to and including the delimiter when the length in the output file
is 0.
If the output file length is not 0, the 1769-ASCII module transmits the number
of bytes/characters specified in the header's length value. The 1769-ASCII
module continues this transmission until the Max Transmit Size is reached. The
transmit delimiter can be set to any valid ASCII character that can be received
over the link.
Be sure to avoid setting the delimiter to a value outside the valid range for your
data bits. For example, a data bit size setting of 7 gives you a delimiter range of
0…127 decimal, 00…7F hexadecimal. Without a valid delimiter, the device
updates the output buffer only on detection of an overflow condition.
Set Up the Receive Character Buffer Length
The Receive Character Buffer Length parameter is the number of characters that
the 1769-ASCII module can receive from the ASCII device into the Input File
buffer. When this value is exceeded, the 1769-ASCII module generates an
overflow, which forces the data into the 1769-ASCII module transmit buffer.
The Produce 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 Produce 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 Receive Character Buffer Length parameter are 0…200. If 0
is selected, the serial port for receiving data is deactivated and header information
in the input file is not updated.
If the total size of the two channels is greater than 200 characters, the Alternate
mode must be used.