As written in another post, I am trying to ram up my 65816 from 12.5 to 17.5 MHz (50 vs. 70 MHz base oscillator clock).
However, either my address decoding (in FPGA, see viewtopic.php?f=10&t=8012#p107250 ) is too slow, or the RAM...

I am currently using a ISSI IS61C5128AS-25 512k x 8 RAM with 25ns access time. As the RAM access, using 1/4th of the oscillator clock (and only the phi2 half of the clock cycle is available) only has 28ns I fear this may be too slow. At least I don't have success....

What RAM are you using when you do your fast (overclocked) 65816 systems? Are there any others faster than that in "classic" TSOP-32?
What I found are others in different packaging, like IS61C5128AL-10TLI (10ns access time) in TSOP-44 (that are actually cheaper at mouser...hm....)

Thanks
André

Edit: according to https://en.wikipedia.org/wiki/Thin_smal ... ne_package TSOP-44 is actually a tad bit smaller even - just with 0.8mm pin pitch instead of 1.27mm.... (do I get a signal routed between the pins still?)

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Author of the GeckOS multitasking operating system, the usb65 stack, designer of the Micro-PET and many more 6502 content: http://6502.org/users/andre/

i personally use the IS61C5128AL-10KLI which are in a SOJ-36 package. for smaller RAM sizes and reusability i use the W24512AK-10 (64kB 10ns) and W241024AK-10 (128kB, 10ns).

also you didn't mention what voltage you need the RAM to run at. i assume 5V because you mentioned the IS61C5128AL series, but you also said you want to use it with an FPGA which are almost always 3.3V.

so for fast 3.3V SRAM you have the IS61WV5128FBLL-10TLI which is pretty damn cheap at almost half the price of the IS61C5128AL-10KLI i mentioned above. it's a TSOP-44 package, but you can also get a SOJ-36 version but it's quite a bit more expensive

on a side note, to avoid having to solder SMT RAM chips like these over and over again you could just make a 4MB SRAM Module (or smaller. for 1MB only populate U1 and U5, for 2MB populate U1, U2, U5, and U6, and for 3MB populate U1, U2, U3, U5, U6, and U7)

Voltage is a good point. Didn't see that the one I mentioned is 5V.
Of course it's 3.3V.

Why are you using SOJ packages? I've gotten quite ok with soldering TSOp and TQFP now. Isn't SOJ even more difficult to solder?

Thanks,
André

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Author of the GeckOS multitasking operating system, the usb65 stack, designer of the Micro-PET and many more 6502 content: http://6502.org/users/andre/

honestly i cannot remember why, maybe it was slightly cheaper back then.
but TSOP is definitely easier to solder and slightly smaller than SOJ (in all 3 dimensions). so really there is no reason to go with SOJ.

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A short update: As it seems I have managed to get my system working at 17.5 MHz, even with the 25ns access time SRAMs. And, according to my scope measurements, the main problem is the time it takes for the data to get from the CPU to the RAM during writes. So, I think a faster RAM may not even help here...

But at least it's good to know there are faster SRAMs, and that they come in different packaging than the 25ns SRAMs... (TSOP44 or SOJ instead of TSOP-32)

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Author of the GeckOS multitasking operating system, the usb65 stack, designer of the Micro-PET and many more 6502 content: http://6502.org/users/andre/