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10-2
Line Current Differential Communications
Date Code 20011112
and Serial Port Communications and Commands
SEL-311L Instruction Manual
change receive data on the rising edge of the receive clock (rising edge of signal RXCB on
DB
-
25 pin 9, falling edge of signal RXCA on DB-25 pin 17).
Table 10.1 shows clock polarity settings for some popular EIA-422 interface communications
equipment.
Table 10.1: EIA-422 Clock Polarity Settings for Popular Communications Equipment
Manufacturer
Product
Channel
Card
Interface
Adapter
DCE Tx/Rx
Clock Polarity
Setting
SEL-311L
Tx/Rx Clock
Polarity
Setting
RFL
IMUX
DS562I
MA406IA
RXICP = Normal
TXICP = Normal
RC422 = F
TC422 = R
Pulsar
FOCUS
64k
N/A
N/A
RC422 = R
TC422 = R
Nortel JMUX
Nx64
Unit
86464-01
86447-90
Transmit = INT
↑
Receive = INT
↑
RC422 = F
TC422 = R
Unlike other interfaces available with the SEL-311L, the EIA-422 interface can operate at either
64 kbps or 56 kbps. The SEL-311L Relay automatically adapts to either data rate. There is no
data rate setting. The transmit and receive clocks must be of identical frequency. This
requirement is satisfied by all commercially available multiplexer equipment.
The EIA-422 standard is not well suited for back-to-back connections because an external clock
must always be supplied. Figure 10.1 shows such a back-to-back connection with an external
clock source. Notice that in a back-to-back connection, the clock source must drive four clock
receivers—one each for transmit and receive clock on each relay. Set the clock polarity as
shown in Figure 10.1 for a back-to-back connection.
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