Will SN74HC245N transceiver support TTL RX when blocked?
If you want the "master" to be able to override the "slave", you need to put the resistor in series with the slave's transmit pin:







simulate this circuit &ndash; Schematic created using CircuitLab

But what you're doing on the "B" side of the '245 is completely invalid. You can't just tie four of the pins together like that.

For receiving, a 4-input AND gate (unfortunately, CircuitLab doesn't have one) combines the signals, assuming that these are UART signals that are high when idle. For the transmit path, individual resistors are used to limit the current when in receive mode.