Re: [Iverilog-devel] Behaviour of tranif when control input is x or z

[Martin W. <mai...@ma...>]

Hi Iztok,

Thanks for this...

Iztok Jeras wrote:
> Hi Martin,
>
> This are NCSIM results.
>
> x x  x x  x x  x x  StX StX  StX StX  StX StX
> ------------------
> 0 0  0 z  0 z  0 z  St0 HiZ  St0 HiZ  St0 HiZ
> 0 1  1 z  1 z  1 z  St1 HiZ  St1 HiZ  St1 HiZ
> 0 x  x z  x z  x z  StX HiZ  StX HiZ  StX HiZ
> 0 z  x z  z z  z z  StX HiZ  HiZ HiZ  HiZ HiZ
> ------------------
> 1 0  z 0  z 0  z 0  HiZ St0  HiZ St0  HiZ St0
> 1 1  z 1  z 1  z 1  HiZ St1  HiZ St1  HiZ St1
> 1 x  z x  z x  z x  HiZ StX  HiZ StX  HiZ StX
> 1 z  z x  z z  z z  HiZ StX  HiZ HiZ  HiZ HiZ
> ------------------
> x 0  x x  x x  x x  StL StL  StL StL  StL StL
> x 1  x x  x x  x x  StH StH  StH StH  StH StH
> x x  x x  x x  x x  StX StX  StX StX  StX StX
> x z  x x  z z  z z  StX StX  HiZ HiZ  HiZ HiZ
> ------------------
> z 0  x x  x x  x x  StL StL  StL StL  StL StL
> z 1  x x  x x  x x  StH StH  StH StH  StH StH
> z x  x x  x x  x x  StX StX  StX StX  StX StX
> z z  x x  z z  z z  StX StX  HiZ HiZ  HiZ HiZ

This seems a sensible result. My test compares the behaviour of bufif0/1, 
pmos/nmos, and tranif0/1 gates in the same circuit - switching a driven wire 
onto an undriven wire. NC-Verilog is showing the same behaviour for the 
corresponding mos and tran gates. For comparison, iverilog (devel) gives:

I/P  BUF  MOS  TRAN
x x  x x  x x  z z  StX StX  StX StX  HiZ HiZ
------------------
0 0  0 z  0 z  0 z  St0 HiZ  St0 HiZ  St0 HiZ
0 1  1 z  1 z  1 z  St1 HiZ  St1 HiZ  St1 HiZ
0 x  x z  x z  x z  StX HiZ  StX HiZ  StX HiZ
0 z  x z  z z  z z  StX HiZ  HiZ HiZ  HiZ HiZ
------------------
1 0  z 0  z 0  z 0  HiZ St0  HiZ St0  HiZ St0
1 1  z 1  z 1  z 1  HiZ St1  HiZ St1  HiZ St1
1 x  z x  z x  z x  HiZ StX  HiZ StX  HiZ StX
1 z  z x  z z  z z  HiZ StX  HiZ HiZ  HiZ HiZ
------------------
x 0  x x  x x  z z  StL StL  StL StL  HiZ HiZ
x 1  x x  x x  z z  StH StH  StH StH  HiZ HiZ
x x  x x  x x  z z  StX StX  StX StX  HiZ HiZ
x z  x x  z z  z z  StX StX  HiZ HiZ  HiZ HiZ
------------------
z 0  x x  x x  z z  StL StL  StL StL  HiZ HiZ
z 1  x x  x x  z z  StH StH  StH StH  HiZ HiZ
z x  x x  x x  z z  StX StX  StX StX  HiZ HiZ
z z  x x  z z  z z  StX StX  HiZ HiZ  HiZ HiZ

i.e. a 'x' or 'z' on the control input of the tran gates turns them off. This 
doesn't seem sufficiently pessimistic to me.

Martin