RKI Instruments M2A - Manual (Page 59)

M2A Transmitter Operator’s Manual 54
Figure 30: Multiple M2As in a Two Branch Configuration
Using the M2A in a 4-wire Modbus System
Although the M2A is a 2-wire Modbus RTU device, it can be used with a 4-wire Modbus controller
if the system wiring is modified as follows:
• Connect the controller’s TxD0 and RxD0 wires together and use this connection as the 2-wire
Modbus D0 signal.
• Connect the controller’s TxD1 and RxD1 wires together and use this connection as the 2-wire
Modbus D1 signal.
• Connect these D0 and D1 signals and the common wire from the controller to the 2-wire
Modbus Network of M2As.
Modbus Mode
Modbus Mode allows you to configure various parameters relating to the Modbus setup of the
M2A. Modbus Mode includes a 5-minute time-out feature. If you do not press a control button for
5 minutes, the M2A automatically returns to normal operation.
NOTE: If the M2A returns to normal operation because of a time-out, it enters a warm-up
period just as it does when it is first turned on.
1. While in normal operation, simultaneously press and hold the DOWN/NO and ENTER buttons
ID = 128
RS-485
M2A
Termination
Jumper
Installed
Modbus
Master
Up to 128 M2As can be connected without a repeater
M2A
Termination
Jumper
Not Installed
M2A
Termination
Jumper
Not Installed
M2A
Termination
Jumper
Not Installed
M2A
Termination
Jumper
Not Installed
ID = 2 ID = 3
RS-485
ID = 1
M2A
Termination
Jumper
Installed
ID = 127
ID = 4