adout decoder 74HC238

[7102]

hi everybody,

I am trying to use decoder ( 3 X 8) (IC 74HC238) for switching. please refer attached image



lets take a case where inputs A0=0,A1=0,A2=0 , EN=1(5v) then Y0=1(5v) was observed, as per my understanding other outs Y1 to Y7 should be zero( 0v) but when i am using this IC with above inputs i observe that Y1 to Y7 pins shows some voltage ( >0.8v) but i need only zero volts at these pins. the same repeats for other conditions such as A0=1,A1=0,A2=0 then Y1=1(5v) and Y0,Y2 to Y7 should be zero(0v) but they show voltage (>0.8v) and this happens for all combination of inputs.

Can anyone tell me why other pins show some voltage( >0.8v) and how to make them to zero?.Is there any alternative IC which gives same functionality with other outputs giving zero(0v).

Awaiting for your kind reply, please help me.


Thanks & Regards,
7102.

 

[barry]

This device has THREE enable inputs, not just 1 (E1*, E2* and E3). Are all three inputs tied to the appropriate voltages?

 

[7102]

hi barry,

Thanks for your reply,

yes, i agree that it has 3 enable pin 2 active low & 1 active high.

now A0,A1,A2 = 0 for that i will have Y0 = 1 (5V),what about the reaming pins output its active low.

if it is active low means how much voltage will be available on the remaning pins.

Thanks & Regards,
7102.

 

[barry]

Active low should be no higher than 0.8v. Check what you have for a load.

 

[7102]

Thanks barry,

i checked with the ic its working fine & meets my application

 

[cameo_2007]

is this solved?

 

[sudheer.k]

respected sir,
how can i convert 4:16 decoder using 3:8 decoder(74HC238) pls post a theard to this........

 

[barry]

respected sir,
how can i convert 4:16 decoder using 3:8 decoder(74HC238) pls post a theard to this........

What? You want to use a 3:8 decoder as a 4:16? Or a 4:16 as a 3:8?

 

[jeffrey samuel]

A 3:8 can be converted into 4:16 never seen the reverse

 

[barry]

A 3:8 can be converted into 4:16 never seen the reverse

How?

If you tie one of the four inputs of the 4:16 low, it will work as a 3:8.

 

[jeffrey samuel]

Not really Barry by using two 3 : 8 we can implement a 4:16 decoder

 

[barry]

Not really Barry by using two 3 : 8 we can implement a 4:16 decoder

You said you've 'never seen' a 4:16 used as a 3:8; I was just explaining to you how to do it. And you're not CONVERTING a 3:8 into a 4:16, you are using MULTIPLE 3:8's to implement your 4:16.

 

[jeffrey samuel]

OOps Misread your post here Barry yeah your suggestion can be effective in case of converting a 4:16 into a 3:8