65816 speed grades

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dominicbeesley
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65816 speed grades

Post by dominicbeesley » Tue Oct 27, 2020 1:31 pm

I'm back to testing against the 65816 in my Blitter project and after some head-scratching as to why it was crashing I've discovered that my 65816's are 8MHz parts not the 14MHz I was expecting (Always read the label :oops: ).

I'd thought that all '816s were 14MHz capable but the one I have here isn't. I can't remember where I got it from but it _is_ an 816 - it does all the 816 stuff well just not quite a quickly as I'd hoped.

I can't find any spec's for an 8MHz part - there are specs for the 14MHz part run at 3.3MHz in the 14MHz part datasheet but I'm suspicious of these - the physical chip I have certainly seems to beat those specs by a large margin but I have no idea how much they might degrade with temperature etc.

Does anyone have a known-good 14MHz DIP 65816 they're willing to swap/sell, I've ordered some from ebay but I'm not holding out much hope.

D

Ramtop
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Re: 65816 speed grades

Post by Ramtop » Tue Oct 27, 2020 1:43 pm

Mouser sells brand new DIP 65C816-14s:
https://www.mouser.co.uk/ProductDetail/ ... JD3DWt8%3D
Gary

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BigEd
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Re: 65816 speed grades

Post by BigEd » Tue Oct 27, 2020 1:48 pm

Oh, that's bad luck. I think yours must be quite an old one. (The '816 in the Communicator is a 2MHz GTE part, marked G65SC816P-2. According to the datasheet they went up to -8 speed grade. Or they hoped to.)

The 14MHz 65816 DIP parts I know about (3 of them) are currently in beeb816 prototype boards, being tested out.

If you don't get any bites here, I think a UK person on the 6502 forums might have one.

dominicbeesley
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Re: 65816 speed grades

Post by dominicbeesley » Tue Oct 27, 2020 2:48 pm

Thanks Ed,

I can't believe I'd not spotted that mine were 8MHz parts a bit dumb really! I'll wait and see what the ones from China look like - I've not done too badly in the past. I'll try the 6502 forums if they prove duff. The one I've got is marked WDC - not sure how to identify what fab made them?

With the 8MHz timings in my board they're actually running at more like 5.5MHz with all the arbitration - I need to sort out/simplify that as it eats up around 50nS most of which I can probably collapse!

D

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BigEd
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Re: 65816 speed grades

Post by BigEd » Tue Oct 27, 2020 2:53 pm

Similarly, we're finding that beeb816 with 55ns SRAM is, on paper, beyond the edge, so a faster RAM might be needed. There's probably a reason why the Beeb at 2MHz was unusually fast (and expensive.) We don't have enough nanoseconds to go round.

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BigEd
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Re: 65816 speed grades

Post by BigEd » Tue Oct 27, 2020 3:00 pm

dominicbeesley wrote:
Tue Oct 27, 2020 2:48 pm
The one I've got is marked WDC - not sure how to identify what fab made them?
A hint of an answer might be here:
http://forum.6502.org/viewtopic.php?p=35662#p35662

cmorley
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Re: 65816 speed grades

Post by cmorley » Tue Oct 27, 2020 5:50 pm

I think I might have a spare 14MHz one bought from Mouser.

Edit: Just checked yes I do. PM me if you want it

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