EPROM suggestions

[msknight]

There are w27c512 eeproms with EPROM pinout that I often recommend.

Please! Recommend away! Grateful for links.

[Paul]

https://www.ebay.de/itm/176099977330
Is the product.
I have no experience with this seller.
I normally buy at the seller
gc_supermarket (247002) which is on holidays until 16th of February

[msknight]

I don't mind waiting for a known good seller. I found their shop, but a search for W27C512 turns up nothing.

[msknight]

Drat. They've de-listed all their items while they're away. (sigh)

[Paul]

On the other side deactivated listings during absence are a sign of good sellers

[1024MAK]

Drat.

Click the picture above...

Mark

[msknight]

Drat.

Click the picture above...
Mark

Well, this is a public forum! I don't want to get banned! Too much good advice

I did just order some of those one time chips from Farnell though, gives me something to play with and mess up.

[msknight]

I've just noticed and registered... if I do the BIOS mod, which requires CE to be tied to ground, then that will stuff up using something like the ZXpand+ because it will want to disable the BIOS by trying to keep that line high.

Do I understand that correctly please?

[Paul]

No need to worry.
Zxpand disables romcs which ist used with a ROM mod.

[1024MAK]

The control signal from the ULA (/ROMCS) goes via a resistor (so that an external device can disable the ROM) to pin 22 of the ROM socket. On a 27 series EPROM, this is /OE (output enable or /G ). The EPROM will only output data if this control line is at a logic low level. Hence it does not matter if pin 20 (/CE - chip enable or /CS - chip select or /E - enable) is always low (connected to 0V/GND).

For the EPROM to drive its databus lines BOTH /OE and /CE must be at a logic low level.

When the external device (ZXpand / ZXpand+ or other device) wants to page out the internal ZX81 ROM, it takes the /ROMCS line high and the EPROM then disables all its outputs.

Mark