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From: John Fields on 1 Dec 2006 11:01
On 30 Nov 2006 13:24:39 -0800, "jimi" <jim_fen05(a)yahoo.co.uk> wrote:

>Does anyone know of an alternative for the 74C925 chip for driving 4x7
>segment LED's. The chip seems to be obsolete. Thanks

---
http://www.1sourcecomponents.com/partinfo/74C925.htm

http://www.intersil.com/cda/deviceinfo/0,1477,ICM7217,0.html

A small microcontroller, however, would be my first choice.


--
JF
From: jimi on 1 Dec 2006 15:29
Thanks for the replies, however, I asked the question so I could avoid
using a microcontroller.

From: Donald on 1 Dec 2006 23:21
jimi wrote:
> Thanks for the replies, however, I asked the question so I could avoid
> using a microcontroller.
>
Thinking out loud,

With simple CMOS technology going away, wouldn't it be wise to replace
it with something you can get in a few years.

Once you get C code running, going to a smaller uC would be easier the
second time.

What ever chip you find today, will be gone next year.

good luck

donald

From: bill.sloman on 2 Dec 2006 01:06

John Fields wrote:
> On 30 Nov 2006 13:24:39 -0800, "jimi" <jim_fen05(a)yahoo.co.uk> wrote:
>
> >Does anyone know of an alternative for the 74C925 chip for driving 4x7
> >segment LED's. The chip seems to be obsolete. Thanks
>
> ---
> http://www.1sourcecomponents.com/partinfo/74C925.htm
>
> http://www.intersil.com/cda/deviceinfo/0,1477,ICM7217,0.html

So you wnat the OP to replace a 16-pin DIP with a 28-pin DIP that
Intersil has marked "inactive".

> A small microcontroller, however, would be my first choice.

I'd prefer a programmable logic part - the 4-digit counter is not
synchronous with the multiplexing logic for the display. Back in 1972 I
dealt with this problem by freezing the multipexing clock until any
incoming count had rippled through the (asynchronous) counters, which
took up to 4usec. This wasn't an elegant solution. With a
microcontroller, I guess you'd rely on the interrupt system to capture
clock increments that occured at the wrong instant, and you'd keep your
interrupt handler short and quick to keep the maximum count rate
respectable.

Programmable logic offers true parallel processing, which can be a lot
tidier.

--
Bill Sloman, Nijmegen (but in Sydney at the moment).

From: Arlet on 2 Dec 2006 02:18

bill.sloman(a)ieee.org wrote:

> I'd prefer a programmable logic part - the 4-digit counter is not
> synchronous with the multiplexing logic for the display. Back in 1972 I
> dealt with this problem by freezing the multipexing clock until any
> incoming count had rippled through the (asynchronous) counters, which
> took up to 4usec. This wasn't an elegant solution. With a
> microcontroller, I guess you'd rely on the interrupt system to capture
> clock increments that occured at the wrong instant, and you'd keep your
> interrupt handler short and quick to keep the maximum count rate
> respectable.
>
> Programmable logic offers true parallel processing, which can be a lot
> tidier.

Many microcontrollers have built-in timers than be driven from external
clock. This isn't truly asynchronous, because the external clock is
typically sampled on the internal clock, but it still allows quite fast
operation. For speeds <= 1MHz, a cheap microcontroller will work fine.

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