[libre-riscv-dev] [Bug 154] Cell for Dependency Matrices is needed

[Hendrik Boom]

On Sun, Jan 12, 2020 at 11:34:23PM +0000, bugzilla-daemon at libre-riscv.org wrote:
> http://bugs.libre-riscv.org/show_bug.cgi?id=154
> 
> --- Comment #2 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
> here is a comparison between the truth tables of SR NOR and SR NAND
> 
> SR NOR
> 
> S R Q
> 0 0 Latch
> 0 1 0
> 1 0 1
> 1 1 0
> 
> SR NAND
> 
> S R Q
> 0 0 *INVALID STATE*
> 0 1 1
> 1 0 0
> 1 1 Latch
> 
> as i suspected there is an inversion of both the output and of the inputs.  in
> many cases both the Q and ~Q are needed, so the negation of output is not
> costing gates.

One is not just the dual of the other; in particular, SR NAND has an invalid state whereas SR NOP does not.
I don't know whether this is an important distinction or a typo.

The other thing I don't know, being a novice in hardware matters,
is what "Latch" means as the output of a circuit.

-- hendrik