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RTU Mode<br />
Query PC Servo Response Servo PC (OK) Servo PC (ERROR)<br />
ADR 01H ADR 01H ADR 01H<br />
Function Code 10H Function Code 10H Function Code 90H<br />
Register<br />
ADD<br />
(HI) 01H Register (HI) 01H<br />
(Lo)<br />
Data length<br />
(word)<br />
00H<br />
ADD<br />
Exception<br />
code<br />
02H<br />
(Lo) 00H CRC(Lo) CDH<br />
00H Data length 00H CRC(Hi) C1H<br />
02H<br />
(word)<br />
02H<br />
Byte counters 04H CRC(Lo) 40H<br />
Data<br />
(HI) 00H CRC(Hi) 34H<br />
0100H (Lo) 64H<br />
Data<br />
(HI)<br />
01H<br />
0101H (Lo) 2CH<br />
CRC(Lo)<br />
CRC(Hi)<br />
BFH<br />
ADH<br />
LRC (ASCII Mode ) and CRC (RTU Mode) Check methods<br />
LRC Checking:<br />
ASCII Mode LRC (Longitudinal Redundancy Check) checking method<br />
The LRC is calculated by adding together successive 8–bit bytes of the message, discarding any carries.<br />
Ex. add ADR, Function code, register address and data contents together, if it get the sum 19DH then discard<br />
carrier ”1” and find two’s complement for 9DH to obtain LRC code.<br />
Ex: Execute diagnostic function for Servo drive ID =01H<br />
STX ‘ : ’ ‘ A ’<br />
‘ 0 ’ ‘ 5 ’<br />
ADR<br />
Data (word)<br />
‘ 1 ’ ‘ 3 ’<br />
‘ 0 ’<br />
‘ 7 ’<br />
Function code<br />
‘ 8 ’ ‘ 1 ’<br />
LRC<br />
‘ 0 ’<br />
‘ B ’<br />
(HI)<br />
‘ 0 ’ END1 (CR) (0DH)<br />
Sub-function<br />
‘ 0 ’ END0 (LF) (0AH)<br />
(Lo)<br />
‘ 0 ’<br />
01H+08H+00H+00H+A5H+37H = E5H<br />
Two’s complement for E5H is 1BH ; derive LRC code: ‘ 1 ’ , ‘ B ’<br />
7-12
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