How to upgrade to a 649 rom?

[Paul]

Thanks for the update.
I got me some CY7C264 as well.
So beeing able to program these would greatly enhance their use

[mikeh_nz]

To read the original ROMs. I use a device called the ZXpand...

Hey Moggy,

I was wondering if you would edit your post here and add this version 550 ROM to the list of files. I didnt see the 550 ROM binary, so I thought I would upload it and try and get into a more centralized location on the forum.

If I understand correctly, this rom version has the infamous sqrt(0.25) bug in it.

[Moggy]

Post updated.

Whilst on the subject it would be more accurate to point out that referring to it as the SQRT bug only is erroneous and it manifests itself much wider than wrongly printing the SQRT of .25 and it would be more accurate to attribute it to errors in other parts of the floating point routines mainly the division routine.

Not that this matters to games players but it was a serious drawback for those of us using the zeddy for actual computing especially mathematics.

Some interesting information concerning this courtesy of maths guru Frank O'Hara found in the links.


https://archive.org/stream/ZX-computing ... 3/mode/2up

https://archive.org/stream/ZX-computing ... 7/mode/1up

https://archive.org/stream/ZX-computing ... 8/mode/1up

This concerning a temporary fix to the borked division routine although it had to be said it didn't work completely as some of the maths were still error prone.

https://www.binarydinosaurs.co.uk/Museu ... /index.php

[mikeh_nz]

Thanks for the update.
I got me some CY7C264 as well.
So beeing able to program these would greatly enhance their use

Paul,

Are you able to erase them and read them back in? Are they all 0x00? Or 0xff?

Im finding all 0x00 and try as I might, so far I am unable to get them to move off 0x00.

[Paul]

Paul,

Are you able to erase them and read them back in? Are they all 0x00? Or 0xff?

Im finding all 0x00 and try as I might, so far I am unable to get them to move off 0x00.

I didn't try yet. I'll try ASAP

[mikeh_nz]

Thanks

Maybe just hook up to a bread board and just see what the byte at address 0x0000 or 0x0001 reads

I think these chips wipe to zero and then you raise the bits (or my chips have been fried from the start)

I’m going to try putting in a voltage regulator and some caps to see if that helps - but I’m likely at the point of giving up. When I do l, I’ll try to add the circuit diagram and the code to see if anyone else has some ideas. I really am ignorant on the electronic side of things and knowledgeable on the coding side.

The only thing I can think of and haven’t tried is a high side transistor driven transistor switch. But I’ve tried connecting one of the data pins to 5v and I still can’t get that bit to flip to 1

[1024MAK]

Most (as in all the working) EPROMs and EEPROMs that I have used contain 0xFF in each location after being erased.

When programming, the bits that need to become logic zero are the ones that are flipped.

What does the datasheet say about it?

Also, do these have a manufacturer and type code/ID? If yes, can you read it? If yes, what result do you get?

Mark

[mikeh_nz]

Thanks 1024MAK

Yeah - that’s my experience with EPROMs too. (Hence the blowing of an eprom)

Data sheet is missing that detail. It’s also missing any timing information for programming. I haven’t seen anything in the data sheet for manufacture type code.

My chips aren’t that old (date codes of 9436 & 9439)

[Paul]

I tried my ROMs on my Retro Chip Tester, they are treated like a 82S641.
All are programmed with the same content.
I tried to erase them, but hadn't had any luck up to now. Data didn't change.
Maybe the eraser is too old. Next Weekend a friend will bring his eraser and I will test again.

The Retro Chip Tester should be able to program the CY7C264 as well. I need to read the manual