User:Carsten Milkau/RS-Latch

RS-latch

An RS-latch is a circuit that stores which of its inputs was last "on". It has typically two inputs: input reset storing value "0" and input set storing value "1", hence the name. It can have multiple outputs, which typically differ mostly in their behavior when multiple inputs are "on" at the same time.

value table

inputs				outputs
reset	set	output1 (previous)	output2 (previous)	output1	output2
0	0	x	y	y	x
0	1	x	y	0	0
1	0	x	y	1	1
1	1	x	y	0	1

It is possible to define a variant with more than two values. The values stored need not necessarily be 0 and 1.

Connectors

• Enabled: if 1, store data, else do nothing.
• Data: input
• Output: stored value

Using Logic Select Unit and Logic Reader

An RS-Latch implemented using two Logic Select Units and two Logic Memory units

This d-latch can store any value. It works in two steps:

1. a Logic Select Unit determines whether to store the last output or the "data" input using the "enabled" input. i.e.

     if enabled
     then store = data
     else store = output

2. a Logic Reader mirrors the value to be stored and feeds it back into the select unit so it can circulate (effectively being stored). This would be obsolete if the select unit could read its own output.

     output = store

Circuit setup

Unit name	Unit type	Connector / Setting	Source / Value
select 1	Logic Select Unit	select	enabled (input)
		0 (input 1)	reader 1
		1 (input 2)	data (input)
reader 1	Logic Reader	in	select 1
		var	setting
		out	output (output)