Message Frame (Protocol) - Mitsubishi Electric 800 Series Instruction Manual

4.5.4

Message frame (protocol)

• Communication method
Basically, the master sends a Query message (question), and slaves return the Response message (response). At normal
communication, the Device Address and Function Code are copied as they are, and at erroneous communication (illegal
function code or data code), bit7 (= 80 h) of the Function Code is turned ON, and the error code is set at Data Bytes.
Query message from Master
Device Address Device Address
Function Code Function Code
Eight-Bit Eight-Bit
Data Bytes Data Bytes
Error Check Error Check
Response message from slave
Message frames comprise of the four message fields shown in the figures above.
A slave recognizes message data as a message by the message data being prefixed and appended with a no data time of
3.5 characters (T1: start/end).
64
PARAMETER