Digital Logic Fundamentals Unit 7 – Tri-State Output
When the EN signal is logic 0, the buffer output is in the high impedance (high-Z) state: the data
input has no effect on the output.
Some tri-state devices are configured to be enabled by a logic 0. The circle on the enable input
indicates this condition, and the ENABLE (EN) INPUT has a not sign. The discussions and
procedures in this unit are based on a tri-state buffer that requires a logic 1 to be enabled.
Tri-state logic devices are very useful for the transfer of data on a data bus. Many tri-state
devices can connect to a data bus. Only the enabled tri-state device sends data to or receives data
from the bus.