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Subject: Re: I need an 8 to 256 decoder or equivalent
Date: Sun, 17 Nov 2002 14:49:11 -0000
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"Si Ballenger" wrote in message
> On Sat, 16 Nov 2002 15:01:02 -0000, "markp"
> >"Gibbo" wrote in message
> >> "David Jones" wrote:
> >> >I'm trying to use an 8 bit binary input to select 1 of 256 different
> >> >LEDS(I'm using leds as an example). I know there exists a 4bit input
> >> >output decoder but I don't know how to get 256 options using it with
> >> >IC's. How do I make the equivalent of an 8 to 256 decoder with the
> >> >discete components? any suggestions are welcome.
> >> >thanks
> >> >david
> >> >
> >> That's going to be big and unweidly.
> >> Instead think multiplexing and 16 X 16 array for the leds.Your
> >> will drop substantially.
> >Yep, use a PLD with 8 inputs and 32 outputs and wire the LEDs as a 16x16
> >matrix. Alternatively, use a pair of 4 to 16 decoders, an inverting
> >and a non-inverting buffer, and wire the LEDs as a matrix. Your 'example'
> >LEDs is a good one because these are diodes, and you need them for
> I'm looking for something similar to attach to a universal IR
> remote control. The remote has a chip that has 12 pins that input
> the button pushes. There are only 32 buttons on the chip, but the
> matrix scheme appears to be 12x12, as the chip pins are connected
> 2 at a time in various combinations via the button pushes. Is
> there a multiplex chip available that could take the 8 pins from
> the parallel port and use them to multiplex the 12 pins on the
> remote to duplcate the button pushes? Below is where I used two
> of the IR chip pins to do a "channel up" button push. Would be
> neat to do all 32 button pushes. thanks.
Sounds like it may be a 6x6 (giving a max of 36 buttons). I would think the
chip scans the buttons by driving low the row pins successively and looking
at the state of the column pins (or the other way round).
What you need to do is have a register writable from the parallel port.
Three of those bits would be the column, three the row. Use a 3 to 8 decoder
for the column (one with an output enable). Use a 8 to 3 bit encoder for the
controller row pins, and compare this result with the row register bits. If
equal output enable the column decode onto the column bits of the
controller. A seventh bit of the regiser would be a 'strobe' bit to enable
the logic. So the row and column bits of the register set up which button
you want to press, and the strobe bit turns that button on. In effect you'll
be simulating a button push by the user.
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