In/Out/In

The term "In/Out/In" describes a specific type of digital logic port behavior, often encountered in integrated circuits or programmable logic devices (PLDs). An In/Out/In port, also sometimes referred to as a bidirectional port with a latching or memory element, functions as follows:

• First "In": Data is input to the port and stored internally within a latch or register. This is the "In" phase.
• "Out": At a later time, the stored data is output from the port. This is the "Out" phase.
• Second "In": The port then reverts to an input state, ready to accept and store new data, overwriting the previous value. This is the second "In" phase.

Essentially, the port acts as a temporary data buffer, capable of receiving data, holding it, outputting it, and then preparing for the next data input. The timing and control of these phases are typically managed by control signals or clock signals.

The key characteristic differentiating an In/Out/In port from a simple bidirectional port is the internal storage or latching capability. A standard bidirectional port switches between input and output modes directly; data doesn't persist at the port itself. In contrast, the In/Out/In port retains the data between the input and output operations.

These ports are often employed in situations where data needs to be temporarily held or synchronized with other parts of a system. Typical applications include interfacing with memory, communication protocols, and controlling external devices.