Latch (electronics)

A latch (English for latch, latch ), or also referred to as state-controlled flip-flop, is a particular version of an electronic one -bit data memory and forms ( e) the basis for wide ranges of digital hardware, especially within the CPU and peripheral chips.

A latch, in addition to the data input of at least one second input (enable or gate ), and in controlling the operating mode: the transparent phase of the output of the latch immediately following the data input; in the hold phase, the last state is frozen before. In addition to this control input, there may be more depending on the model, such as a reset input, like the global to all these acts Einzellatches at several latches in a chip.

In contrast to edge-triggered flip-flops a latch during the entire active stroke phase is transparent, ie input changes can affect the output immediately.

Truth table

With a positive logic, the following truth table is typical ( D is the data input D of the enable input, L and H, the two logic levels, X is any logic level and Q0 of the last D- level prior E = L):

General classification

Latches are sometimes called " latch register ", but are no registers in the proper sense, which are generally defined as edge-triggered flip-flops.

In the TTL - series logic chips there are, among others, the latches 7475, 74100, 74116, 74373, 74375 In addition, there are other variants, some with more inputs. Intel 8212, Intel 8282, Intel 8283rd

In today's microelectronics, which works almost exclusively edge-triggered, loose latches steadily in importance. IBM and Intel, however, still develop most circuits with latches as the basic element.

To further relationship, the sample and hold circuit is one in analog technology ( Sample & Hold).

Latches as an error of publication

If you used to latch the term as a verb, so it often means a malfunction of a digital hardware circuit. She stays in a particular state stuck ( " this condition is latched " ), although the input signals do not actually require a change in the output state. Cause of such a festival slopes can be overloading of individual circuit components, a race condition or thermal influence.

  • Digital technology