Latch vs register

Archiver

Hi All, can someone explain to me the difference between a latch and
a register, is a latch constructed of flip-flops, so that after it
has been accessed it will need to be reset?

thanks, mark

Archiver

The 'base' object here is a flip-flop (F-F).
Flip-flops come in a few flavors. The 'D'
flip-flop 'clocks' its Data ('D') input
to its Q output when its Clock input rises.

This is also called a 'latch' -- the input
can be changing, but the value on the input
when the Clock rises is 'latched' to the
output. The output then does not change
until the next Clock rise.

A 'register' is typically one or more
'latches' -- 8 being a typical number.

The 'D' F-F also has 'Set' and 'Reset'
inputs. Normally low, when 'Set' goes
high the 'Q' output goes to 1. 'Reset'
high sets the 'Q' output to 0. When you
get a register bank of these, you can 'Set'
or 'Reset' the entire bank with one signal.

So: the short answer:
Yes, a latch is constructed of 'D' f-f.
No, after it has been 'accessed' it does not
need to be reset -- it can hold the earlier
value until a new value is loaded into it.

--- In basicstamps@yahoogroups.com, "lakewood5982003" <598@m...>
wrote:
> Hi All, can someone explain to me the difference between a latch
and
> a register, is a latch constructed of flip-flops, so that after it
> has been accessed it will need to be reset?
>
> thanks, mark