This device can easily achieve bidirectional switching, but care must be taken for bus buffer output conflicts and input floating.
Although this bus buffer allows the signal direction to be switched easily, the following considerations apply:
Fig. 1 shows the equivalent circuit of the bi-directional bus buffer (74VHC245), and Table-1 shows the truth table.
When /G is "H" level, all input/output terminals are floating, so it is necessary to pull up to the power supply or pull down to GND.
Table-1 Truth table of Bi-directional bus buffer (74VHC245)
The following describes the timing requirements using the circuit and timing diagrams as shown in Fig. 2.
A bidirectional bus buffer is connected between the A bus and the B bus. In the initial state, the A pin is an input, and the B pin is an output. Therefore, a signal is transmitted from the A bus to the B bus. At this time, Buffer Y is disabled (i.e., provides no output).
The internal circuit changes its mode while the DIR pin changes state (from Low to High or High to Low) and while the enable pin (/G or /OE) changes state. During these periods, the output value is indeterminate, meaning it cannot be determined whether the output is High, Low, or between High and Low. Take this into consideration when creating a design since the output value during these periods cannot be guaranteed.
The following documents also contain related information.