Which 32k ram chip to use?

[msknight]

I'm reading up about the internal 32k ram upgrade and about some ram being too fast and requiring capacitors to slow down the signal wires.

Grateful for people's pointers to the ram chips to use please, and the most reliable/straightforward installation instructions

My intention will be to fit a socket, and then put the chip in another socket in order to ease the wiring between various pins.

[msknight]

For reference, for the BBC B sideways 4 bank ram, I'm using the Alliance AS6C1008-55PCN and I'm not needing any additional components.

[1024MAK]

Yeah, but that's a different architecture (the control signals between 65XX and Z80 systems are rather different, as are the timings of these signals).

Plus, it's the ZX81 display access that's the problem with the faster modern CMOS SRAM chips, not the normal read access. The ZX81 uses the Z80 to get the display file data to feed the parallel to serial shift register (part of the ULA), but also uses the Z80's DRAM refresh cycle to perform part of the work of generating the video image.

Typically, the normal ROM video generation works, it's just the high resolution graphics used by games where due to the slight mismatch in timing when a faster modern CMOS SRAM chip is used, you get garbage on screen rather than the intended graphics.

For a older, and hence slower SRAM chip, maybe this one:
https://www.ebay.co.uk/itm/276023856391 (HITACHI HM65256AP-15)

This seller is normally reliable, at least, with the items I have bought from them in the past.

Mark

[msknight]

Thanks Mark.

I've ordered a few.

Are there any easy ways to check if the RAM chips are OK please? I know I have a RAM tester for the BBC Micro chips, but that's not going to work with these I think.

Still waiting for the Luamcode to HDMI to arrive... probably next year now by the looks of it!

Michelle.

[1024MAK]

Some EPROM programmers can test SRAM chips. That's by far the easiest and fastest way.

There are also special chip testers, but if you don't already have one, you would have to buy one.

As you have a BBC Micro, you could test using a spare sideways ROM socket and some of the clip-on test leads. Either copy various ROM images across from disk to the SRAM and check they work okay, or use a machine code program to write a test pattern and read it back. You can't use BASIC, because BASIC runs from it's own sideways ROM.

It's also possible to hang a SRAM chip off an expansion port of a computer, and test it that way, but this does involve lots of wires and some control circuitry.

I did this when just for fun, I wanted to test a 2114 SRAM chip using a ZX Spectrum:

2114 SRAM chip tested using a ZX Spectrum

2114 SRAM chip tested using a ZX Spectrum

Mark

[msknight]

I did this when just for fun, I wanted to test a 2114 SRAM chip using a ZX Spectrum:

I'm seriously impressed!

[msknight]

I was looking for the datasheet and came across this which might be helpful for people in the EU wanting chips... I'm not sure...
https://electols.com/shopping/en/ic/108 ... ap-15.html
...perhaps someone could validate this find.