2 chip TOS possible easily in C070243 rev F?

[PhilC]

Evening All.

Just trying to get the STM upgraded to take tos2.06 or EmuTOS so that I can put a TF536 into it. The main issue is that the 256k/1mbit rom jumpers are not present on this board.

Can anyone point me in the diection of a How to guide? I've had a quick Google but with no luck so far. The main difference seems to be needing a 74ls11 and A15 & 16 connected up.

[stephen_usher]

Dos the machine have the standard MMU?

If so then you can use the circuit in the STFM schematic as a basis. The extra logic is simple.

[EzdineG]

@PhilC
I have the same non-jumpered ST (rev. B in my case) as you and am currently awaiting delivery of an over the rom socket ROM switcher PCB from JLCPCB I hacked up. I plan to use one in conjunction with @agranlund's blitter board and will try feeding it ROM2 as I won't run < 2.0.

I'm not going to bother merging the CE if I can get away with it.

If it works out, I'd gladly send you one of each.

[agranlund]

I don't think you can get the (CPU) A16-A17 from the rom sockets on those motherboards which lack the jumpers for the 1M mode so you would have to fetch them from somewhere else.

So assuming you're using 32pin eproms of some sort, have one in a LO socket and the other in a HI socket (with necessary wiring to make up for the different pin count and layout between 28pin mask roms and 32pin eproms).

pin3 (A15) on both roms to pin44 (A16) on CPU
pin2 (A16) on both roms to pin45 (A17) on CPU
The other address signals are available from the rom sockets.

Pin24 (/OE) on both your roms goes to GND.

Then for /CE, you can copy the Atari schematics for motherboards that do have the rom jumpers:
/ROM0-2 from Glue to a 74LS11. The output is the /CE for both your roms (pin22).

rom5.jpg

I *think* you get the Glue /ROM0-2 signals from pin 20 of Rom LO0-2 / HI0-2 on those motherboards that don't have the rom jumpers. One schematic I found had it like that anyway.. If this is the case for you then that is a lot easier than trying to wire them from the Glue.

None of this is something I tried myself and anything written above could be nonsense.. feel free to slap me around if I wrote something incorrect :)

My motherboard had those rom solder-jumpers & a slot for the 74LS11, so I had easy access to that single /CE + A16-A17 from the CPU when I did my first 6x 28pin Maskrom TOS 1.00 -> 2x 32pin Eeprom TOS 1.04 upgrade with some pretty crude hacked together sockets and wires :)

Best is to compare the ROM portion of these schematics:
https://dev-docs.exxosforum.co.uk/1040ST ... 6-1987.pdf
https://dev-docs.exxosforum.co.uk/520ST_Schematic.pdf

The above doesn't give you TOS2.06 of course, it's only for being able to use 2x 32pin eeproms instead of those 6 mask roms.

I plan to use one in conjunction with @agranlund's blitter board and will try feeding it ROM2 as I won't run < 2.0.

I think just feeding it ROM2 should do the trick as long as you don't care about TOS 1.xx :)

[exxos]

I may still have some of these PCBs about if it helps

https://www.exxosforum.co.uk/forum/viewt ... f=16&t=276

That converted 6 chip to 2 chip.

[PhilC]

Thanks for the suggestions guys, I'm still deciding what to do exactly.

I may still have some of these PCBs about if it helps

https://www.exxosforum.co.uk/forum/viewt ... f=16&t=276

That converted 6 chip to 2 chip.

@exxos what would be required to use those with Tos2.06? Just the decoder logic?

[exxos]

Thanks for the suggestions guys, I'm still deciding what to do exactly.

I may still have some of these PCBs about if it helps

https://www.exxosforum.co.uk/forum/viewt ... f=16&t=276

That converted 6 chip to 2 chip.

@exxos what would be required to use those with Tos2.06? Just the decoder logic?

Yeah I guess so.