Date Code 20010625
Line Current Differential Communications
10-3
and Serial Port Communications and Commands
SEL-311L Instruction Manual
SEL-311L
CHX/CHY
DB25
TXDA
2
TXDB
14
RXDA
3
RXDB
16
RXCA
17
RXCB
9
TXCA
15
TXCB
12
COMMON
7
Settings:
RC422X=R
TC422X=F
SEL-311L
CHX/CHY
DB25
2
TXDA
14
TXDB
3
RXDA
16
RXDB
17
RXCA
9
RXCB
15
TXCA
12
TXCB
7
COMMON
Settings:
RC422X=R
TC422X=F
DWG: M311L082
A B
Clock Source
Figure 10.1: Back-to-Back EIA-422 Connection With External Clock Source
CCITT G.703 Codirectional Interface
The G.703 interface is transformer isolated from the chassis to 1500 V rms. Since each
differential pair is transformer isolated, there is no signal common. To prevent ground loops,
ground the cable shield only at the multiplexer. Refer to Table 2.2 for the G.703 cable
appropriate to your application. All of those cables connect the shield at the multiplexer end
only. The DB-25 connector pinout on the SEL-311L Relay and the direction of signal flow is
shown in Figure 2.7.
For relay-to-multiplexer connections, use the
SET X
or
SET Y
commands to make setting
TIMRX = E (TIMRY = E for Channel Y). No clock polarity selections are necessary because
the synchronizing clock is embedded in the transmit and receive data. A typical relay-to-
multiplexer connection for a G.703 interface is shown in Figure 2.7. The multiplexer must
provide a clear channel (64 kbps) for use with the G.703 codirectional interface. If your network
or multiplexer equipment cannot provide a clear channel, contact the factory.
For back-to-back connections, use the
SET X
or
SET Y
commands to make setting TIMRX = E
(TIMRY = E for Channel Y) in one relay, and TIMRX = I (TIMRY = I for Channel Y) in the
other relay. The relay with TIMRY = E synchronizes to the relay with setting TIMRY = I,
providing error free operation. Connect the relays as shown in Figure 10.2.
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