4. Communications
4.5.3 Command Code: 03, Read Content of Register (T, C, D)
Example: Read coils T20~T27 from Slave ID#01
PC→PLC “: 01 03 06 14 00 08 DA CR LF”
Sent message:
Field Name ASCII
STX :
Slave Address 01
Command code 03
Starting Address Hi 06
Starting Address Lo 14
Number of Points Hi 00
Number of Points Lo 08
Error Check (LRC) DA
END 1 0D (Hex)
END 0 0A (Hex)
PLC→PC
“:01 03 10 00 01 00 02 00 03 00 04 00 05 00 06 00 07 00 08 B8 CR LF”
Feedback message:
Field Name ASCII
STX :
Slave Address 01
Command code 03
Bytes Count 10
Data Hi (T20) 00
Data Lo (T20) 01
Data Hi (T21) 00
Data Lo (T21) 02
Data Hi (T22) 00
Data Lo (T22) 03
Data Hi (T23) 00
Data Lo (T23) 04
Data Hi (T24) 00
Data Lo (T24) 05
Data Hi (T25) 00
Data Lo (T25) 06
4-15