RS485 is a half-duplex communication standard, must be controlled to a good bus transceiver state. RS485 inputs are open or has been terminated and no driver U1 and U2 will make it to the receiver output (RO) is high. Differential inputs A1 and B1, if the input byte data, the U1 side of the RO will produce a voltage jump, locked by the trigger 74HC74 and 74HC00 NAND gate state machine at the falling edge of the RO ON state. The state machine will be U2's driver Enable Pin (DE) pull is high, the input data bytes forwarded out from the U2 RS485 level.
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