Rockwell Automation 900 Temperature Controller Communications Functions - Series B - Manual (Page 63)

Publication 900-UM004D-EN-E - July 2010
Modbus Communications Procedure 4-5
No Response
In the following cases, the received command will not be processed and a
response will not be returned.
Consequently, a timeout error will occur at the host device.
· The slave address in the received command does not match the
communications unit number.
· A parity error, framing error, or overrun error occurred due to a
problem such as a transfer error.
· A CRC-16 code error occurred in the received command frame.
· There was a time interval of more than 3.5 character times between data
packets that make up the command frame.
Furthermore, the specified function’s processing will be performed but no
response will be returned for broadcast functions (slave address = H’00).
Function List The following table lists the function codes.
Table 4.4 Function Code List
Function Code Name Process
03 (H’03) Read variable
(multiple) This function reads from variable areas.
It is possible to read two or more consecutive
variables.
16 (H’10) Write variable
(multiple) This function writes to variable areas.
It is possible to write two or more consecutive
variables.
It is also possible to broadcast this function
(broadcast transmission).
06 (H’06) Write variable
(single/operation
command) This function writes to the variable area and writes
operation commands.
It is also possible to write to a single parameter by
specifying the address in 2-byte mode. (This is not
supported in 4-byte mode.)
It is also possible to broadcast this function
(broadcast transmission.)
8 (H’008) Echoback Test This function performs an echoback test.