Serial Transmission Modes; Modbus Master Operation Via Serial Interface - JUMO mTRON T Manual

4.1

Modbus master operation via serial interface

If the central processing unit has been configured as a master, it can send requests on the bus
to slaves. Complete frames are always transmitted here. The corresponding Modbus and de-
vice addresses must be specified when configuring the frames in the setup program. For each
frame, it is possible to enter the device address and Modbus address used to request the value.
Each programmed frame can be disabled by selecting the "Modbus slave" setting for the "in-
terface" parameter.
A maximum of 8 frames can be enabled for reading and maximum 8 frames for writing. The
enabled frames are cyclically processed consecutively. This also applies to writing frames re-
gardless of whether a process value is changed or not. This rules out a transmission that de-
pends on the condition of a change. The complete frame is always transmitted with the frame
length configured in the setup program.
NOTE!
Double writing of a target variable, e.g. the same variable selector in two read frames, will
lead to undefined states and must be avoided.
Timeout
Indicates the maximum time-out used for each sent command to wait for a response before the
next command is carried out.
Scanning cycle
The scanning cycle defines the time interval used to read in variables.
Number of external inputs during Modbus master operation
If Modbus master operation is selected, the number of input and outputs is limited to
• 64 float, integer, and binary values and
• 9 texts (27 texts as of system version 02; 90 texts as of system version 04).
The external texts can be read into the central processing unit and provided to the optional mul-
tifunction panel as a batch text.
Interface parameters
frame configuration
8 read
frames
8 write
frames

4 Serial transmission modes

+
Driver
(base unit)
RS232/
RS485
Modbus
slave
Modbus
slave
49