Acksys MI400 Series Technical Documentation Manual page 72

STATUS OF EIA/TIA-562 (RS232), RS422A/485 SIGNALS
VOLTAGE
BINARY STATE
CONDITION
FUNCTION
CHARACTERISTICS OF RS422A-RS485 SIGNAL IN IDLE STATE
EIA RS442A/485
+ TX
- TX
+ RX
- RX
NOTE:
In an idle state, differentials signals +TX and +RX are at a lower potential than
signals -TX and -RX.
This remark is particularly important when connecting other RS422A-RS485
interfaces. In effect, there is considerable confusion concerning the idle state in which
the line should be found, and in the names for signals +TX, +RX, -TX and -RX (A, A',
B and B') in the various interfaces of different manufacturers.
NEGATIVE POSITIVE
1
MARK
OFF
- CCITT V11
A A has a lower potential than B in the idle
B state (1, MARK or OFF)
A' A' has a lower potential than B' in the idle
B' state (1, MARK or OFF)
0
SPACE
ON
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