Chip to Sequentially Read Many Inputs ?

B1ackwater wrote:

> An embedded project I'm working on requires the ability to
> read the status of up to 64 input ports - but obviously I
> want to use as few of my microcontroller pins as possible.
> Somewhere I heard of devices called 'sequencers' or something
> like that where you just feed it a clock signal and it turns
> on individual i/o pins in order and then wraps around to pin
> zero again (or is reset with a third line - which would seem
> better since you'd KNOW the thing would re-start on pin 0). 
> 
> Something like this would be ideal since it would only consume
> three i/o pins on my controller. However, a quick google search
> didn't reveal any such devices. Maybe I'm not using exactly the
> right name for the things ? I'd heard of something like it for
> scan-writing to those big 60-odd-pin LCD chips, but I'm 
> interested in READING a logic 0 or 1. Reset -> Read Pin 0 ->
> Clock -> Read pin 1 -> repeat -> repeat -> repeat(N) -> reset.
> 
> Any info helpful. Reply to group. 

have a look at:
http://www.dontronics.com/pipex.html

something I did with shift registers years ago, but it gives you the 
schematic and code examples, if you want to try shift registers.

Don...

-- 
Don McKenzie
E-Mail Contact Page:       http://www.e-dotcom.com/ecp.php?un=Dontronics

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["Followup-To:" header set to sci.electronics.misc.]
On 2005-10-10, B1ackwater <bw@baark.net> wrote:

> An embedded project I'm working on requires the ability to
> read the status of up to 64 input ports - but obviously I
> want to use as few of my microcontroller pins as possible.
> Somewhere I heard of devices called 'sequencers' or something
> like that where you just feed it a clock signal and it turns
> on individual i/o pins in order and then wraps around to pin
> zero again (or is reset with a third line - which would seem
> better since you'd KNOW the thing would re-start on pin 0). 

if it's an output it'd be a decade counter, one pin to advance the high
signal, one pin to reset it to it starting place, 10 outputs,

if you want to read try a parallel-in serial out shift register,

typically 8 inputs  one output pin, one pin so signal the chip to read 
the inputs, and one pin to get the next input, the also have an input whare
you can attach the output of another shift register... so they can be 
daisy-chained (plugged into the back of each other) so you could line
up 8 of them and read the whole 64 inputs only three pins on your micro.

 try 74HC165

if you can matrix your inputs you may be able to lower the chip
count by using a decade counter to select rows and a single shift 
register to read columns - it'd use more i/o pins though  

Bye.
   Jasen

On 2005-10-10, Jim Granville <no.spam@designtools.co.nz> wrote:
> B1ackwater wrote:
>
> The HEF4021 can read 8 ips, and drive 3 ops, so you can matrix 24
> buttons on one of those. They are under 20c.

neat, with the addition of a 3-bit address decoder you could matrix 64
buttons without using any more uC pins than are needed to drive the HEF4021

Bye.
   Jasen

bw@baark.net (B1ackwater) wrote in news:434a62cb.6492746
@news.west.earthlink.net:

> An embedded project I'm working on requires the ability to
> read the status of up to 64 input ports - but obviously I
> want to use as few of my microcontroller pins as possible.
> Somewhere I heard of devices called 'sequencers' or something
> like that where you just feed it a clock signal and it turns
> on individual i/o pins in order and then wraps around to pin
> zero again (or is reset with a third line - which would seem
> better since you'd KNOW the thing would re-start on pin 0). 
> 
> Something like this would be ideal since it would only consume
> three i/o pins on my controller. However, a quick google search
> didn't reveal any such devices. Maybe I'm not using exactly the
> right name for the things ? I'd heard of something like it for
> scan-writing to those big 60-odd-pin LCD chips, but I'm 
> interested in READING a logic 0 or 1. Reset -> Read Pin 0 ->
> Clock -> Read pin 1 -> repeat -> repeat -> repeat(N) -> reset.
> 
> Any info helpful. Reply to group. 
> 
> 

See what you can do with these circuits : 
http://members.shaw.ca/roma/switching-2.html
roma