74HC138 and 74HC238 Proteus model

[jayanth.devarayanadurga]

74HC138 and 74HC238 Proteus model is incorrect. If somebody has the right model please upload it. The pins E1 and E2 are inverted and E3 is normal in datasheet. In model E1 is normal and E2 and E3 are inverted.

Can anybody fix the model.

 

[FvM]

I don't understand what you're complaining about.

There's a (meaningless) difference in pins names, at least in some vendor's data sheets, but input polarity is correctly assigned to pin numbers.

 

[jayanth.devarayanadurga]

I checked 4 different datasheets. All have the same pinouts. It's a Proteus model error. See page 2 here. **broken link removed**

E1 and E2 are bubbled inputs and E3 is normal. In Proteus model, E1 is normal and E2 and E3 are bubbled.

 

[FvM]

There's no "error", I think.

E1 to E3 are just arbitrary names. I don't see a relevance of keeping it. The important point is to have the non-inverted input at pin 6.

 

[alexan_e]

if the names of the pins are a problem then you can create a new schematic symbol ( actually a small edit in the existing one ).
Ignoring the pin namings do they operate as shown in the symbol ( the invered ones as inverted and the non inverting as non inverting)?

 

[jayanth.devarayanadurga]

No the model is not working. I connected E1, E2, E3 together to a logic toggle and tried giving 1 and 0. The outputs doesn't change state.

 

[FvM]

I connected E1, E2, E3 together to a logic toggle and tried giving 1 and 0. The outputs doesn't change state.

As expectable according to the built-in logic.

 

[alexan_e]

No the model is not working. I connected E1, E2, E3 together to a logic toggle and tried giving 1 and 0. The outputs doesn't change state.

Seems fine to me


enabled


not enabled

 

[uavmax]

it work pretty mutch here is the isis file atached.

 

[jayanth.devarayanadurga]

How to control the outputs by using one line for all the 3 ENx pins? I need extra NOT gates? Is there any similar 74HCxxx or CD40xx device which has only one pin to enable/disable outputs? I need to completely turn off the outputs without changing the output state i.e., If I turn off and turn ON the outputs the output should be restored with the previous state.


Edit:

Even if device exist which doesn't remember the previous output state will also do after all after turning OFF the outputs I change the state of the outputs.

 

[Venkadesh_M]

Hi 74138 is decoder a combinational circuit which never going to remember anything, If you want add a d latch or do it differently....

 

[FvM]

The intended function isn't quite clear in terms of digital logic.

Maybe HC137/HC237 can do what you want.

P.S.: It should be clear, that the HC138/238 enable function can be always controlled with a single pin, by strapping the other pins to a fixed level.

 

[jayanth.devarayanadurga]

I am doing nothing special. I want to use it to turn ON/OFF particular SSD out of 8 SSDs. The output is shifted one bit a time like CD4017 which selects the SSD. For turning OFF the display I need to disable the output of the 138/238 so that all SSDs turn OFF before displaying next digit. So, the o/p state doesn't have to be same as previous state as I change the o/p of 138/238 but I need the o/ps to be turned OFF colmpletely in between changing the digits.

 

[Venkadesh_M]

Going to design CC or CA?? What is your connection, Did you used inversion or directly connected?? When using CC and 74138 will be perfectly matched.. in between change in output just disable the decoder with Enable pins...

 

[FvM]

Referring to your previous post, of course the HC138/238 outputs will return to the previous state if the selection (input A/B/C) is kept. Sounds like you are asking for an obvious feature of the said chips.

 

[alexan_e]

How to control the outputs by using one line for all the 3 ENx pins? I need extra NOT gates?.

P.S.: It should be clear, that the HC138/238 enable function can be always controlled with a single pin, by strapping the other pins to a fixed level.

What FvM said does exactly that, maybe you missed his point.
You can connect both the inverted enable pins to gnd and then use the remaining one as the enable pin (1 will enable outputs and 0 will dissable) or if you need an inverted logig connect the non inverted enable pin to +5, one inverted to gnd and use the remaining inverted enable pin with inverted logic.