hi
i want to use pass transistor to design 4 to 1 switch and use vhdl
hat somebody help me?
thanks

> pass transistor
Can you specify what is meant by this term?
A bidirectional 4:1 multipexer?

Lothar Miller schrieb:

> A bidirectional 4:1 multipexer?

yes.the task is to design inputswitch use pass transistor instead of use 
multipexer.

So you have a component "pass transistor"?
Or do you have to describe such a "pass transistor"?

i have no component.so i have to do it

all fb can be 2and or 2nand .use switch to choice a inputsigal to fb and 
output too in same fb.

> something like this?
The bidirectional behaviour is missing in this description  :-/

> i have no component.so i have to do it
So this looks like very low-level design. If you want to describe a 
bidirectional switch, most of the work will be the resolution 
function.
Given the three ports A, B and C you must handle e.g.
what happens if A = '1' while B = '0' and C = '1' (open)
or
what happens if A = '1' while B = '0' and C = '0' (closed)

            A
 
            |
          |-
    C ----|
          |-
            |
            
            B

So such a pass transistor may look this way:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity PassTransistor is
    Port ( A : inout  STD_LOGIC;
           B : inout  STD_LOGIC;
           C : in  STD_LOGIC);
end PassTransistor;

architecture Behavioral of PassTransistor is
begin
  A <= 'Z' when (C='1') else
       '1' when (B='1' and C='0') else
       '0' when (B='0' and C='0') else
       'X';
       
  B <= 'Z' when (C='1') else
       '1' when (A='1' and C='0') else
       '0' when (A='0' and C='0') else
       'X';
end Behavioral;

In a simplified way by using the resolution function od std_logic you 
can write

  A <= B when (C='0') else 'Z';
  B <= A when (C='0') else 'Z';

> all fb can be 2and or 2nand .use switch to choice a inputsigal to fb and
> output too in same fb.
I urge you to get known to the terms and phrases used in your business. 
In your picture theres absolutely no bidirectional path, so its just a 
straight forward mux.
Have a look at the code posted by berndl, thats a mux.

But i don't clearly understand your picture. When you have 4 function 
outputs and afterwards a mux to 4 signals, which of the outputs must be 
routed to which signal. Can you scetch one or two signal paths in your 
picture?

this is a test path . 2 inputs and 1 output

What happens here with the other 6 inputs and 3 outputs?

In your sketch you have 4 dual inputs, 4 function blocks and 4 outputs. 
This results in 64 possible routings, how can you handle this with a 2 
bit input? The main problem to understand is why you have 4 outputs.

Lothar Miller schrieb:


<What happens here with the other 6 inputs and 3 outputs?

other 6 inputs and 3 outputs do nothing.because only one funktion block 
aviable with the switch

> other 6 inputs and 3 outputs do nothing.
"Nothing" is no option. For shure they will do something  ;-)

OK, lets give the kids some names:

inputs     functions   outputs
in0a          fb0        out0
in0b

in1a          fb1        out1
in1b

in2a          fb2        out2
in2b

in3a          fb3        out3
in3b

Are the only routing possibilities e.g. in0 - fb0 - out0
or in1 - fb1 - out1 ...

Or can e.g. the in0 ever be routed to out3 through fb2?

Lothar Miller schrieb:
>> other 6 inputs and 3 outputs do nothing.
> "Nothing" is no option. For shure they will do something  ;-)
>
> OK, lets give the kids some names:
>

> inputs     functions   outputs
> in0a          fb0        out0
> in0b
> 
> in1a          fb1        out1
> in1b
> 
> in2a          fb2        out2
> in2b
> 
> in3a          fb3        out3
> in3b
> 

> Are the only routing possibilities e.g. in0 - fb0 - out0
> or in1 - fb1 - out1 ...
inoa in0b  fb0 out0


> Or can e.g. the in0 ever be routed to out3 through fb2?
this can be in3a in3b fb1 out3 too

> this can be in3a in3b fb1 out3 too
So it will be
inXa inXb   fbY  outX     with (X=0..3, Y=0..3)
but never
inXa inXb   fbY  outZ     with (X=0..3, Y=0..3, Z=0..3, Z/=X)


So how do you select one of the 4 input pairs to one of the 4 fb input 
pairs (these are 4x4=16 possible ways) with only 2 bits?

> ... dass man sich damit schwer schlagbare Konkurrenz schafft.
Glaube ich nicht, bzw. macht mir keine Sorge   ;-)

Lothar Miller schrieb:
>> other 6 inputs and 3 outputs do nothing.
I think it should work like this:
- One of the "2-inputs" on the left should be switched to the input of 
ALL function blocks in the middle (the rest three left inputs are 
ignored)
- One of the FB outputs schould then be selected as output (the rest are 
High-Z, don't cares or holding the last output)

Probably for a testing devices/input one after the other with just 
needing the 4 Input blocks once.

Grashalmlängenkontrollminister schrieb:
> Looks like homework...
I agree with that especially the terminus 'pass transistor' more sounds 
like he should construct a complex-cmos-device than a VHDL code...

Because when my assumption is true, this task could be more easily be 
acomplished by a pipeline than by such a strange 
"pass-transistor-design"...