Chapter 5 Relay Ladder Logic Programming
109
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12B
MU (Modbus) (SG2-20Vxxx model only)
MU function performs Modbus RTU communication at RS485 port. There are 15
MU coils: MU01~MU0F.
Remote IO and IO Link have higher priority than MU to use RS485 port. MU is
executed when the remote IO setting in the system is disabled (No Remote IO) and ID
isn’t 0.
There can be several MU commands executed at the same time, but only one command can be performed, the
rest are postponed until the performed one is accomplished.
Function mode corresponding communication function code:
mode Communication
function
code
1
03 (read registers)
2
06 (write single register)
3
10 (write multiple registers)
4
01 (read coils)
5
05 (write single coil)
The coils used for MU function:
M3D: Received
M3D turns ON after received, then check-up for error. Transferring data to
target address if there is no error.
M3E: Error flag
communication error flag
M3F: Time out flag
M3F turns ON when the master does not get any response from slaver within
certain time. M3F will automatically reset if M3D reset.
The time of time out depends on the baud rate as shown in the below table.
Baud rate (bps)
Time out (ms)
4800
、
9600
、
19200
、
38400
125
57600 100
115200 80
There are 5 parameters in MU function as shown below.
symbol Description
①
MU mode (1~5)
②
ID number of the target unit: range from 0 to127
The address of target register in that unit:
1) address is assigned to a constant, range from 0000 to ffff;
•
Just do the read/write function to the register with one data
length/address in mode 1 and 3.
•
Do the read/write function to the coil with one data length/address
in mode 4 and 5.
③
2) The address refers to the content of DR coil, and the value of coil
behind this one determines how many register or coil will be read or
write, see the next five pages for more information.
④
DR code, store sending/receiving data from this DR
⑤
MU code (MU01~MU0F)
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