Black Box ME540A-ST, Manual, Page: 12 / 26

FOM LINE DRIVER—ST AND S M
1 1
4.3 RS-485
Follow these instructions to set up the RS-485 interface.
1.
Connect the wire to the terminal block.
Set the wire to TB1 (the 4-wire terminal block) as indicated
below for 4-wire RS-485 applications:
Position 1 ------Receive B positive
Position 2 ------Receive A negative
Position 3 ------Transmit B positive
Position 4 ------Transmit A negative
For 2-wire RS-485 applications, tie Transmit A negative to Receive A negative and Transmit B
positive to Receive A positive. See the illustration below.
2.
Set S5.
Move S5 to the RS-485 position, B*. S5 determines which circuit is tied to TB1.
3.
Set W4, W5, and W6.
For 4-wire operation:
W4 and W5 are in the A-B position (as shipped). When configured for 4-wire, W6
is not used.
For 2-wire operation:
Move W4 and W5 to the B-C position. W6 is now used to set the time the driver
will remain enabled after the transmission of the last data bit (see below).
A ----------7-msec. delay
B ----------2-msec. delay
C ----------0.7-msec. delay
D ----------0.15-msec. delay
4.
Set S1.
If the RS-485 receiver needs to be terminated, move S1 positions 7 and 8 both ON. Note that
both switches must either be ON or OFF simultaneously.
To terminate:
Position 7 ------1 (terminated)
Position 8 ------1 (terminated)
Not terminated:
Position 7 ------0 (unterminated)
Position 8 ------0 (unterminated)
*Factory default.
RXB (+)
RXA (-)
TXB (+)
TXA (-)
KEY
0 = Open/Off
1 = Closed/On