Impressions of ATmega1281/ATmega2561 Products

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I'm curious to hear from some of you who are using or are planning to use the ATmega1281 or ATmega2561 and their derivative low voltage products.

Do these newer chips interest you or do you find the ATmega128 to be sufficient? What compelling reasons, if any, do you have for wanting to switch?

Let me know your thoughts...

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The biggest issue I found with the ATMega128 is that it is limited to 3 hardware JTAG breakpoints. I don't believe that is the case with the 1280/1281, but I've not yet tested that.

Edit: I found this document from Atmel for porting from ATMega128 to 1281 gives an overview of the differences between the two devices: http://www.atmel.com/dyn/resourc...

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I had been using both, and I prefer 1281 for many reasons. Since for high volume price is quite similar, i would go for the 1281. 8KB of RAM and two extra timers are key issues for me. Also 16MHz @3V3 is also a good point if you need HP.

Guillem.
"Common sense is the least common of the senses" Anonymous.

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Quote:
it is limited to 3 hardware JTAG breakpoints.
Is that a limitation of the chip or the JTAG debugger?

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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The ATmega128 always had a problem with breakpoints. I can't remember exactly where I saw it documented.

These new features appear to have been overlooked in the migration document.

The new SPMCSR register SIGRD function. The 1281/2561 allows your software to read the chip signature using SIGRD. This makes it possible to have the chip's software configure itself in real time by probing the actual chip identity/type. If you do not want real time configuration and you have products that use mixed chips from this newer family, common bootloader code can be smart about automatically guiding the correct firmware into the right size chip, without having to depend on something added like preprogrammed EEPROM chip identity values.

You can write directly to the 1281/2561 PIN register to simply invert an output pin state. This is nice if you bit-bang an output pin.

There are 3 new General Purpose I/O registers (GPIOR) in the 1281/2561. GPIOR0 is within the 0x1F bit SBI, CBI, SBIS and SBIC instruction limit.

Pin 1 is not wasted in the new 1281/2561.

Timers 4 and 5 exist in the 1281/2561, but the 64 pin package does not support any input/output pins. Still, if you want two extra software/interrupt 16 bit timer/counters run off of the AVR internal clock, you have them both available. The new power reduction register lets you shut down their power consumption if you do not want to use them.

"Compelling" is only valid in the context that your own requirements create. However, there are significant new capabilities in the 1281/2561.

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Guillem Planisi wrote:
I had been using both, and I prefer 1281 for many reasons. Since for high volume price is quite similar, i would go for the 1281. 8KB of RAM and two extra timers are key issues for me. Also 16MHz @3V3 is also a good point if you need HP.

Is that right? I'm looking at moving from a Mega64 to a Mega1281, simply because I could use the extra RAM, but I wasn't aware that it would run at 16MHz on 3V3. The datasheet on the Devices tab at AVRFreaks seems to contradict this.

Four legs good, two legs bad, three legs stable.

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John, you are rigth. I double checked the datasheet I have, and I was wrong. Thanks to point me in the right direction. How could I be this wrong, a 'brain fart'? I'm getting old...

Thanks.

Ah, and also thanks to Mike, I didn't know that feature to read the signature.
I used timers 4 and 5 for software timming (ModBus timeouts/retries, and system tick), that allows other timers to be used for other, more HW related purposes. In fact, I wrote an RTOS for this uC that uses timer 5 as the scheduler clock.

Guillem.
"Common sense is the least common of the senses" Anonymous.

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js wrote:
Is that a limitation of the chip or the JTAG debugger?
The chip.

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Thanks... I appreciate all of your input. I had read the migration guide produced by Atmel, but I'm glad to read some end user opinions.

With the newer chips, is Atmel looking to wind down production levels of the 128?

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Quote:
With the newer chips, is Atmel looking to wind down production levels of the 128?

It seems unlikely, over the histroy of the AVR8s the only ones put out to pasture so far are:

http://www.atmel.com/dyn/product...

All the old stalwarts like mega8, mega8515, mega8535, mega16, etc. are still alive and kicking even though there may well be more modern "upstarts" that provide a better solution of cost/performance benefit.

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Quote:

All the old stalwarts like mega8, mega8515, mega8535, mega16, ...

I must really be getting old. The old stalwarts were the AT90S4433 and AT90S8515 and AT90S8535, and then along came that new-fangled ATmega163...

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Oh no I was just picking random examples of "the old school" not trying to document an exact "timeline" ;-)