ProSoft Technology MVI56E-GSC - Normal Data Transfer; Block Request from the Processor to the Module

MVI56E-GSC/GSCXT ♦ CompactLogix or MicroLogix Platform Reference
Enhanced Generic ASCII Serial Communication Module User Manual
ProSoft Technology, Inc. Page 85 of 140
April 24, 2017
4.3 Normal Data Transfer
Normal data transfer includes the transferring of data received or to be
transmitted on the ports and the status data. These data are transferred through
read (input image) and write (output image) blocks. Refer to Sample Logic
Program for a description of the data objects used with the blocks and the ladder
logic required. The following topics describe the function and structure of each
block.
4.3.1 Block Request from the Processor to the Module
These blocks of data transfer information from the ControlLogix processor to the
module. The structure of the output image used to transfer this data is shown
below:
Port 1
Byte Offset
Description
0
Block Sequence Number (Read Block Byte 499 value sent by module)
1 to 2
Intercharacter delay for this message (milliseconds between characters)
3 to 4
Number of characters to transmit on Port 1 (0 to 200)
5 to 204
Port 1 data to transmit
205 to 250
Reserved
Port 2
Byte Offset
Description
251 to 252
Intercharacter delay for this message (milliseconds between characters)
253 to 254
Number of characters to transmit on Port 2 (0 to 200)
255 to 454
Port 2 data to transmit
455 to 495
Reserved
To set up a message to be transmitted, the simple example ladder expects the
user to do the following in this order, either manually or by writing additional
process logic:
 Load the character codes for the outgoing message string into the controller
tag GSC.Px_Data.WriteString (where x = 1 for Port 1 or 2 for Port 2)
 Set the tag GSC.Px_Data.WriteLength to the number of characters to send
Once the number of characters to transmit in the write block is set greater than
zero (value in word at bytes 3 & 4 and/or 253 & 254), the ladder logic program
will trigger the Process Write Block function and move a new sequence number
value into Byte 0 of the output image. This Block Sequence Number will be the
value received in the most recently received Read Block. If the selected port is
not already busy, the data in the block will be moved to the port’s transmit buffer
and sent out the port.