Re: RS latch and D flip-flop

Ed Casas (edc@ece.ubc.ca) Wed, 6 Dec 2000 22:19:20 -0800 

Date: Wed, 6 Dec 2000 22:19:20 -0800
From: Ed Casas <edc@ece.ubc.ca>
Subject: Re: RS latch and D flip-flop



> Is it possible that we are asked to use RS latch to control a
> state machine instead of using a D flip-flop ?

No.  RS latches are not widely used for digital logic design
these days.

> For the Guarage Door question in the assignment, should we draw
> a D flip-flop in the schematic diagram...? (because it was not
> drawn in the solution handout)

There would be two flip-flops (FFs).  Their D inputs would be
connected to A' and B' and their Q outputs would be A and B.
Their clock inputs would both be connected to the same clock
signal.

> Can we use RS labth instead of D flip-flop in the controller
> for this question...?  If we can, could you simply explain
> how...?

No, you can't use RS FFs to build the types of state machines
that we've been designing because RS FFs don't have clock inputs
(you need to add logic to an RS FF to make it into a D FF).

-- 
Ed Casas   edc@ece.ubc.ca   http://casas.ece.ubc.ca   +1 604 822-2592