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3-2-2. Combinational Logic: Bidirectional Bus Buffers

Example of application of a bidirectional bus buffer

Bidirectional bus buffers (transceivers)
Example: 74VHC245

A bidirectional bus buffer (transceiver) is a type of logic circuit whose I/O pins can be configured as input and output to receive and transmit data.
Since a transceiver allows the signal direction to be changed via a control signal (DIR), it is used along a bus line through which data are transferred bidirectionally.
The following shows an example of application of a transceiver.
When using bus signals bi-directionally, connect both the bus input and bus output to V_CC or GND via a pull-up resistor to prevent the input signal from becoming open (undefined) when the signal is switched by the control signal (DIR).
Please be careful not to short-circuit the output with the output of the bus line when switching signals.

Combinational Logic: Bidirectional bus buffers

The direction of the A and B pins can be changed easily by changing the value of DIR while /G is High.

Change the value of DIR and the direction of external data while /G is High.
During period #0, data are transferred from B to A.
During period #1, the A pin assumes the High-Z state. Therefore, output data are invalid.
During period #2, change the value of DIR and the direction of external data.
During period #3, enable the A and B pins. Then, output data stabilize at the beginning of period #4.
During period #4, data are transferred from A to B.