27512 / 28C512 / 28F512 / 29C512 / 29F512 compatibility

[bverstee]

I'm new to QL (but not new to Sinclair: http://www.ByteDelight.com), and digging into QL enhancements and add-ons.

I fixed my QL yesterday with the help of a Minerva ROM I borrowed.
Now I want to clone this ROM, and as I always do, I immediately think of how to make 10 or more for others too.

So I'm looking for the cheapest 64K x 8 ROMs.
My universal programming doesn't like 27xxx chips, so I need EEPROMs or FLASH alternatives.
I think these are direct options:
- 28C512: €4
- 28F512: €2
- 29C512: €3
- 29F512: unavailable

Or maybe I'll use 128K x 8 (1024Kb) when these are cheaper to obtain.
- 29C010: €1 !!
- 29F010: €3

But I need to make sure the above types are compatible.

I will google for it, but like to share this investigation with others.

[bverstee]

29C010 must be usable, but has 4 more pins.
This is not a real problem as the Minerva ROM is already on a pcb, so I will focus on the 29C010.
Time to order some.

[prime]

I used a 29x040 in my QIMI project allowed me to have banked ROM with selectable OS versions.

29x010 should work fine, if you put a jumper on A16 to pull it high and low you could have Minerva in one half of the ROM and another version in the other....you can of course do the same with an 040, and add A17, and A18 to have multiple versions.

I've also used an 010 to replace a 27128 in the cartridge slot, by connecting pins 1,2,32,31,30, and plugging in the flash rom (in a 32 pin socket) with pins 1,2 & 31,32 overhanging (but connected by a wire to pin 30 (pin 28 of the rom cart socket) as above.

The pinout is mostly compatible I think it's just A14,15,16 that are in slightly different places, because of the /WE pin.

Cheers.

Phill.

[bverstee]

Great, thanks!

I read that the Minerva ROM can also be used externally, but the internal ROMs should be removed.
Isn't there any way to disable the internal ROMs by external circuitry on the ROM port?

I have to start investigating the schematics myself of course.
I just can't believe at the ZX Spectrum the internal ROM could be disabled, but on the QL this is not possible.

[prime]

Great, thanks!

I read that the Minerva ROM can also be used externally, but the internal ROMs should be removed.
Isn't there any way to disable the internal ROMs by external circuitry on the ROM port?

I have to start investigating the schematics myself of course.
I just can't believe at the ZX Spectrum the internal ROM could be disabled, but on the QL this is not possible.

You have to believe it

The same ROMCS line goes to the external ROM port as to the internal sockets, it's effectively the same "ROM bus". Remember initially the QL OS was designed to be a single 32K ROM, then it was found it would not fit so the ROM dongle was added (to the already designed in ROM port) with the extra 16K of ROM, in that situation they would have to both be active together. Later of course the additional 16K was fitted internally.

You could fit a switch to the ROMCS of the internal ROM to allow you to disable it but this would still mean opening the machine up.

Cheers.

Phill.

[1024MAK]

In some versions of the QL, the same ROMCS line goes to both the internal ROM chips and the ROM port.
In this case, as far as the internal ROM chips are concerned this works fine. As the mask ROM chips can be specified to have their CS pins active high or active low, an address line is fed to a second CS input.

If you want further details, shout out. It may take me two to three days to locate my notes on the QL ROM socket pin-out.

Mark

[belg4rion67]

29x010 should work fine, if you put a jumper on A16 to pull it high and low you could have Minerva in one half of the ROM and another version in the other....you can of course do the same with an 040, and add A17, and A18 to have multiple versions.

Cheers.

Phill.

As reported by Phill, I've used a 29C010 with two different OS: in the first half I've burned Minerva+TK2, in the second one JS + TK2 and with a simple switch linked to A16 pin, I can choose before power on (and even during reset..) what OS starts after.... and all works perfectly!
Ciao!
Paolo

[RWAP]

Shame the 27C010 couldn't be used - I have plenty of those....

[bverstee]

It can, but my 'modern' cheap Chinese programmer has troubles with them old 'high-voltage' programmable chips.

It's hard to obtain a good universal programmer: it's either looking for a cheap one that supports the most old and new components, and accept that it has some minor flaws (like with 27xxx EPROMs, and a 32 bit version of Windows is needed for mine, so I run a VM on all my 64 bit machines for that), or pay hundreds for a well-known brand programmer.

I choose the first: for parts that are hard (or simply not) to program with my TOP2005, there are great alternatives, which are almost always cheaper too (the 29C010 turns out to cost less than 1 EUR!).

One other advantage of EEPROMS or FLASH ROMs is that they can be programmed (updated) from a machine itself, e.g. the DivMMC EnJOY! interface's ROM.