PA 7400
Technical description Chapter 8
36
Fig. 8-4: Enabling the RS 422 transmitter
•
Make sure
that the values of data bits D1-D7 are not overwritten when writing
in the MODEM CONTROL REGISTER A(B) on
Base-S1(2) +4
.
Controlling the RS 422 receiver
You control the RS 422 receiving component with bit
RD-EN-1(2)
.
•
Set
jumper J16(7) on pos. B
.
Bit
RD-EN-1(2)
is the bit D1(3) of address
Base-S1 +7
of the DUART
component.
RD-EN-1(2)
= 0
Reception is possible (reset value)
RD-EN-1(2)
= 1
Reception is not possible
Terminators and open-circuit potential for RS 422
The receive lines RxA+(RxB+) and RxA-(RxB-) are in RS 422 at an open-
circuit potential through 1 K ohm resistors.
If the board is located at the end of the network
•
insert
a terminator through jumper J18(13)
.
J18(13) in pos. A
120
Ω
terminator
J18(13) in pos. B
100
Ω
terminator
IMPORTANT!
If the board does not receive data, and if you want to detect whether a
line interruption has occurred (damaged line, no device connected),
•
invert the open-circuit potential
of the receive lines RxA+(RxB+) and RxA-
(RxB-).
Set
the jumpers as follows:
J19(14) in pos. A
J20(15) in pos. B