2. Modbus-RTU (RS-232)
This program is to support Modbus-RTU protocol by using RS-232 communication and It is able to data setting
and external control of PR-DTC-4100.A(D). It uses RS-232 communication terminal at terminal block. Please be
sure not to confuse serial port at board side.
1) Modbus-RTU Frame
Start (logical) Address Field Function Field Data Field CRC Check
28 bits (3.5 Character times) 1 byte 1 byte n x 1byte 2 bytes
2) Function Code
Function code is a collective code of command which is offered by Modbus protocol. It is able to read or write
the values of Slave Memory (Coil, Register).
Code 1/16-bit Description I/O range
03 (0x03) 16-bit Read holding registers 40001 - 50000
06 (0x06) 16-bit Write single register 40001 - 50000
16 (0x10) 16-bit Write multiple registers 40001 - 50000
3) Exception Code
In case it happens errors such as undefined Function Code, Address, and data setting of range not permitted,
please set the values which add 0x80 from Function Code to be an error code to respond.
Code Name of error Description
01 (0x01) Illegal function It appears when requesting unpermitted operation.
02 (0x02) Illegal data address It appears when requested data address is not valid.
03 (0x03) Illegal data value It appears when requested data is beyond the bounds.
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