Mitsubishi Electric MAM-AM20, Instruction Manual

Page: 24 / 48

Setting the operating mode on the DIP switch
NOTE RS485 stipulates that the cables should be terminated at both ends of the transmission sec-
tion. The termination prevents signal reflections in the cables and in times of no data trans-
mission, enforces a defined idle state on the bus. This termination can be implemented
using, for example, specific resistors at the screw terminal. It can also be implemented via
the DIP switches on the Mitsubishi Alarm Modem.
RS422 Connection
RS485 2-wire connection (2-wire bus system, half-duplex)
In this operating mode, transmit cables and receive cables are interconnected. If the Mitsubishi
Alarm Modem is installed at the beginning (first station) or end (last station) of the bus system,
the bus system must be terminated by setting the DIP switches accordingly.
RS485 / RS422 Interfaces
4 - 4 MITSUBISHI ELECTRIC
COM2
Device B
T–
T–
T+
T+
(0
V)
R–
R–
R+
R+
Fig. 4-7:
The receiving lines are to be connected to
R+ (other end T+) and
R- (other end T-),
the
sending lines to
T+ (other end R+) and
T- (other end R-)
according to the opposite sketch.
Operating mode DIP 1 DIP 2 DIP 3 DIP 4 DIP
Two-wire RS485 with termination 1 1 1 1 1111
Two-wire RS485 without termination 0 0 1 1 0011
Four-wire RS485 without termination 0 0 0 0 0000
Four-wire RS485 with termination of receive cable 1 1 0 0 1100
RS422 0 0 0 0 0000
Tab. 4-1: Setting the operating mode on the DIP switch
Bus Master
COM2 Slave 1
(0
V)
R–/T–
R+/T+
Slave 2
R–/T–
R+/T+
Slave 3
R–
T–
R+
T+
T– R– T+ R+
Fig. 4-8:
The twisted pair cable is to be connected to
T+ to T+ or R+ and for
T- to T- or R-
according to the opposite sketch.