Electronics > Microcontrollers

Replacing an Atmel 90S1200

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I have a product in production, since 1997. It uses the 90S1200, SOIC-20 package.

The function is simple:

- wait for an input to go 0 to 1 (interrupt; wakes up the CPU)
- set an output pin
- read a 4 bit dipswitch, calculate a timer delay
- run the timer,
- reset the output pin
- go to idle mode

The reason for the sleep is to reduce power, because I am running the chip with a 4MHz ceramic resonator (PBRC-4.00AR  AVX). The oscillator runs all the time though, IIRC.

So, a very simple job. It was written in AVR assembler, assembled with a batch file under DOS. We production program the boards with an AVR programmer:

The 90S1200 went on a last time buy 10+ years ago and I bought loads then, £0.50 each :)

Later I went to redesign the board with the supposed replacement, the 8313, only to find Atmel dropped it by the time I got around to it. I think they may still do it in some tiny package. I still have enough 90S1200 for a year or two but ought to look at a redesign. The trouble with Atmel is that by then they will drop whatever chip I go for :)

Can someone recommend a cheap chip which is likely to be around for many more years, draws low power like the 90S1200 (2mA active, 0.4mA idle), runs off 5V, and isn't BGA?  I am not using the EEPROM and in fact the 90S1200 had corruption issues there (1st location only, IIRC). It also needs to be easy to "get into"; I don't want something weird.

The 90S1200 needs an external reset controller and I am using one of the Seiko SOT-23 chips to do that. That costs another 30p or so, and it is silly; the CPU ought to have a robust power-on reset internally.

The timer calculation (shortest time delay is 100us) needs to be accurate to 1% so internal RC oscillators are marginal at best.

Many thanks for any pointers.

Could you maybe use an LDO to 3.3V if you could drop the external reset circuitry?
Btw: PIC16F84 is still available and started in 1996. I think using one of the new Microchip PICs is the most practical solution. I assume they won't obsolete something they have just released.

If it should be an AVR the ATtiny20 or Attiny24 would be likely OK. Ideally get a layout that can use both types - I think this should work.
These type are relatively popular though already relatively old.  Even if they run out, chances are new chips would use a similar pin-out.

For some strange reason the tiny204 and similar don't seem to support an external crystal, which is a bit anoying.

Chances are the 2 kB version should be large enough even when writing the program in C.

If low power is relevant and a lower clock is OK I would reduce the clock, e.g. a 533 kHz resonator or even a 32 kHz watch cystral.
Chances are they would still have the classic errata of not haveing the internal caps working.
A reduced voltage (e.g. 3 V)  also helps.

With a very new chip one never knows if that type really gets popular, if not it may as well disappear fast. However chances are the case / pinout would follow some common pattern.

Microchip doesn't seem to retire old PIC's; they just get more expensive.  I have no idea about Atmel chips, but the 5-digit 16F PIC's are the latest (16F18xxx, 16F19xxx).

Also, look at the timing accuracy required.  The internal oscillator in many newer MCUs is now accurate enough for many interval timing applications.  e.g. Microchip PICs with calibrated oscillators that can hold better than 1% accuracy at nominal voltage and room temperature, and no worse than 2.5% over their full voltage range and extended temperature range have been available for a decade or so now.  If that's good enough, you should also be able to eliminate the resonator.


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