TC Communications TC3420, Руководство пользователя

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Two-wire RS-485 is a half-duplex operation, which means transmit and receive operations take turns; they
do not operate concurrently. From the user’s point-of-view, the channel is in receiving mode when no data
is transmitted from the remote unit. The local RS-485 transceiver will change to transmitting mode (Tx mode)
upon receiving the first bit of data from remote unit. The local RS-485 transceiver will stay in Tx mode until
a predetermined period (transition time; generally used by the customer's device) elapses after the last bit
is received from the remote unit. The TC3420 automatically adjusts internally for that specific transition time.
(See figure 4)
Four-wire RS-485 is a full-duplex operation, which means transmit and receive operations function
concurrently. From the user's point-of-view, both channels are in the receiving or transmitting mode at all
times. (See figure 5)
The RS-485 Driver/Receiver transition time is determined automatically by the TC3420 unit internally. The
local unit's RS-485 transceiver changes to transmit (Tx) mode upon receiving the first bit of data from the
remote unit. The transition time is the amount of time before the local unit's RS-485 transceiver will revert
to the high-impedance receiver mode after the last bit is received from the remote unit. The RS-485 transition
time automatically adjusts internally by the unit, according to the user's device timing.
* Note: Not used, for future release.