Hi All

Is it possible to combine more for example 3-to8 line or a 4-to-10 line decoders, to get a 7-to-128 line decoder for 7-bit?

Electronics4you
__________________________________________________ ____________________________
"Be cool"

 

yes i believe you can do that..
what are you trying to do??

 

The CD4514 is a 4 to 16 line decoder. You could make a 7 to 128 decoder with additional logic to decode the other 3 bits, but it is more work than I want to tackle right now.

__________________
see my website: www.geocities.com/russlk

 

I believe you can do that. did you mean to say an 8-to-256 line decoder instead of 7-to-128 decoder?
it's gonna be very complex circuitry! if you can get it on a single chip the better.

__________________
Everybody can but not everybody will.

 

Its probably better making your own decoder using logic gates instead, but still, it will be complex circuitry.

and why a 7 to 128 decoder?

__________________
-=: The best low-priced components to troubleshoot with are the speaker and the LED :=-

 

Presumably because 7 bits gives 128 seperate values?.

But as williB asked, knowing what he's trying to do would be helpful?.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

I have a 128 lenght display, where I can write to the line that I want, without usign a shift register, which runs trough all bit all over again.

 

And there's 128 seperate wires to it?, sounds like a poor design?.

The multiplexer solution is simple, these multiplexers were originally designed for memory addressing, so you treat them accordingly.

Connect one 3 to 8 multiplexer to the top three address lines (in your case bits 4, 5 and 6 of your 0-6 bits). Each output will select one lower 16 bit page of addressing.

Connect eight 4 to 16 bit multiplexers all to the lower 4 bits (bits 0, 1, 2 and 3), and the enable bits of each to the outputs of the first multiplexer. You now have 128 (8 x 16) individually addressable pins - and LOT'S of wires 8)

It's standard memory addressing for micro-processors, used to address EPROM, RAM, and I/O.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

I also have the same question about any type of 7-128 or 8-256 decoder? I need about more than a hundred parallel outputs for logic signal. It is like control the parallel port of a PC but the port have only 8 data pins (D0 - D8), so I have to think about a decoder. Any suggestion please ?

 

hi nobtiba,

Attached a block diagram of a 'Set 1 of 255 high' selector.
NOTE: the Group selector ic is a 4515, the rest are 4514

This should give you the general idea.

If you want to select analog lines, look at the HEF4067 ic.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Here is an expander for the parallel port. The circuit can be duplicated and C2, C3 used to get up to 394 outputs. The address of the '573 is put on the lowest 4 bits of the data bus and strobed in. The data for that '573 is put on the data bus and the '4514 enabled.
http://www.geocities.com/gpg212/parport128.2.gif

 

Hi Ericgibb,

What is the difference between HEF4515 and 4514? Why don't we just use one type for both group selector and the rest ?

 

hi,
The 4514s require a /E [pin23] to select the ic, so a 4515 outputs will give a LOW on the selected line.

I understood you wanted to SET a 1 of 255 output HIGH [+V] ,thats why I suggested 4514, as a 4514 will go HIGH when selected.

Is this clear?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

I want to control the output either on or off. I do not know what does it mean by "with input latches" in HEF4514 datasheet. I just want to enable the IC by an input signal to "enable pin".

Is there any optional for 4-to-16 decoder? I search the whole day at the electric shopping center for 74HCT4514 but could not find it. So I think I should better to have alot of options.

Thanks.

 

hi nobtiba,

>> I want to control the output either on or off. I do not know what does it mean by "with input latches" in HEF4514 datasheet. I just want to enable the IC by an input signal to "enable pin".

The input latch 'EL' pin on the 4514, if connected high, will enable any change on the A0 to A3 pins to immediately 'select' an output pin, the latch is 'transparent'.
If the EL pin is connected low, any change on the A0 to A3 pins will not change the selected output pins.
Whatever the states of A0 to A3 were before EL went low will be be stored in the latch.

When you say "control the output either on or off" do you mean when you have SET the output 'low or high' on an output,
you want it to stay in that state while you control another output pin, high or low ????
If so, this is an important change in the logic required.

>> Is there any optional for 4-to-16 decoder? I search the whole day at the electric shopping center for 74HCT4514 but could not find it. So I think I should better to have alot of options.

What decoder ic's can you get??

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/