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Commodore m55, anyone got one?
05-18-2018, 01:02 PM (This post was last modified: 05-19-2018 07:36 AM by blackjetrock.)
Post: #1
Commodore m55, anyone got one?
I have finally got my hands on a Commodore m55, albeit in broken form when I got it. I fixed it up and got it working, I have a video here if you're interested:

https://youtu.be/HOy0yVGiYTk

Now, I got the calculator going and was trying various things out and I got to the gallons/litres conversion function. When I converted 1 gallon to litres I got the expected answer: 4.54 or so. Hmm, hang on a minute, that's the expected value for me as I'm in the UK. I checked the manual and the figure it quotes for the conversion is 3.7854 or so. So my calculator doesn't agree with the manual. I'm pretty sure my calculator was a UK purchased one so it has a US value in the manual and a UK conversion factor. Does anyone over in the US have a Commodore m55? Could you try converting a gallon to litres and see what you get?

I didn't notice a jumper to switch US/UK on the PCB but there could have been, I suppose. Are there any internal photos of US m55s on the web anywhere?

Does this mean I don't have a complete set of 60 series Commodores?
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05-19-2018, 07:07 AM (This post was last modified: 05-19-2018 07:09 AM by EdS2.)
Post: #2
RE: Commodore m55, anyone got one?
Those are amazing keyboards!

Makes sense to me that a Made in England calculator would have UK conversions: it would be a bug otherwise! Commodore made their own chips, so the constants would be in their own mask ROM - they could conceivably have a bond out option, or a tie off, but I wouldn't be surprised if there was a US ROM - if indeed this calculator was ever sold in the US.

BTW I think you meant to link this video:
https://www.youtube.com/watch?v=HOy0yVGiYTk

Cheers
Ed
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05-19-2018, 07:41 AM
Post: #3
RE: Commodore m55, anyone got one?
(05-19-2018 07:07 AM)EdS2 Wrote:  Those are amazing keyboards!

Makes sense to me that a Made in England calculator would have UK conversions: it would be a bug otherwise! Commodore made their own chips, so the constants would be in their own mask ROM - they could conceivably have a bond out option, or a tie off, but I wouldn't be surprised if there was a US ROM - if indeed this calculator was ever sold in the US.

BTW I think you meant to link this video:
https://www.youtube.com/watch?v=HOy0yVGiYTk

Cheers
Ed

Yes, I'm almost certain this is a UK calculator. There must be a US one though as the manual has the US constants. Commodore did make their own chips,I have a die shot of a calculator that has theior logo on it, even Casio has Toshiba on their chips. I'll have another look and see if there's a jumper somewhere, I think it would be odd to have an entire different ROM just for a single value, but maybe not. There is a diode on the back of the main chip, but I assumed a rework, maybe that's it? If someone has a photoof a US calculator PCB then I could compare it.
I'm not sure where the ROM is on these calculators either, as the N60 and M55 have the same PCB and chips, except the M55 has an extra one. I assume it's RAM as it has more memories. So the ROM may be an OTP, as the part numbers on the main chip are the same. Or, the ROM is in a couple of extra chips on the PCB. I may have a go with a logic analyser and see what traffic is going on between the big chip and the smaller ones.

And yes, sorry, the video URL was wrong, I've fixed it in the original post.
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