Cutler-Hammer D320 PLC, User Manual

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D320 PLC User's Manual
The Structure of the Communications Frame
Query and Response Frame
The frame is sent from the source address (SA) by the sender to the destination address (DA), the
receiving device. For the query (Q) and the response request (RR), the SA is the address of the
peripheral device, and the DA is the address of the PLC to which the message is being sent. For the
query answer (QA) and the response (R), the PLC becomes the sender of the message, and so the PLC
address is the SA and the peripheral device’s address is the DA.
Query Acknowledge Frame
Response Request Frame
Response Frame for an Error
Length of the
information field (byte)
1-255:1-255 byte
0:256 byte
CRC-16 code
(2 byte)
Function Code
Sender ID Number
Receiver ID Number
DA SA FC Length Information CRC L CRC H
Constant
DA SA $00 01 00 CRC L CRC H
Error #1 Wrong communication
function code
Error #2 Out of range
Error #3 Wrong frame structure
Error #4 CPU did not perform
Error #5 Frame too long
DA SA $8X 01 Error CRC L CRC H
Constant
DA SA $80 01 00 CRC L CRC H