Piggy-back eproms on 4-in-1 OS board?

[Gunstar]

While in the midst of getting ready to program (burn) the 27512 eprom for the Dropcheck 4-in-1 OS board, I am having difficulty in picking out just 4 OS's for it, I had a thought that maybe I didn't have to be restricted to just 4 OS's for the 4-in-1 board by piggy-backing two 27512's onto the board and having an extra toggle switch to change between the two eproms as well as the toggle switches to change between the OS's on the selected eprom. I made a crude sketch of what I had in mind to post to get confirmation or not if this would work or not from others who are more experienced than I in the OS rom area. I did a piggy-back OS mod to my Atari Jaguar a couple of decades ago, and IIRC, without looking up that mod instructions or opening up my Jaguar, it was pretty much this simple.

 

So would this work? And if not, can I make it work another way? Are there other pins that might also have to be diverted through a toggle switch?

Edited September 1, 2019 by Gunstar

[JR>]

I always find this picture helpful:

 

 

You could also use a 27010 or 27020.  You'd need to reroute VCC to the proper pin, and possibly /PGM depending on the chip.  Then it's just a matter of toggling the additional Axx lines, preferably with pull-up resistors.  When you get to that many switches, old SCSI ID switches or BCD or HEX thumb-wheel switches come in handy.

 

If you choose to piggyback you also have the option of toggling /OE (output enable) or /CE (chip enable - preferred) instead of un-powering one of the chips.

Edited September 1, 2019 by JR>
more info

[Gunstar]

@JR> Thanks for the diagram. As for the toggle switch, that was mostly for simple display purpose and I plan on using some 4/6/8 switch DIP switches I have for OS selection and if I needed to toggle more than just chip power or /CE. 

 

 For this job I'll be using 27512's as that all I have on hand and I'd rather not have to reroute anything more than I have too, and have as few toggle switches as I can. Not to mention the fact that my eprom burner is only 28-pin and works only with 2764-27512 eproms, and 2732 with an adapter. But I think I will take your suggestion of using the /CE line to toggle eproms, as then I'd only need a SP/ST toggle switch.👍

 

Thanks for the idea of the 128K/258K 27010/020's though, I may go that route in the future if I ever do a similar OS upgrade with DIY multi-OS board, and of course upgrade to a TL866II+ burner. For now, between my R.D. XL/XE 27xxx eprom burner and all the Atari/PC flash tools like Uflash and Maxflash cart studio and other device-unique "studio flashers" and Atarimax programmer cart, SIO2PC,etc., at my disposal to reprogram flash chips used in Atari external add-ons, I've no current need to upgrade to a TL866 as all my current bases are covered with what I already have for what I need.😎

Edited September 1, 2019 by Gunstar

[Gunstar]

Actually, I guess it would need a DP/ST toggle switch, right? ...it's late and I'm tired, so I'll think about that in the morning...err, later this morning, as it's already 2:30 am here...

Edited September 1, 2019 by Gunstar

[JR>]

For /CE? an SP/DT center grounded with pull up resistors on the /CE pins.

[Gunstar]

Thanks. I thought I wasn't thinking clearly so late last night, I had it backwards with the switch! At this point I'm still working with the eprom burner, with initial set-up. learning the program and proper settings, adjusting voltage levels on the pots, etc.. I then attempted to burn twice, with errors on loading into the buffer before actual burning occurred, so my eproms are still empty/erased (I have no UV light box to erase). Apparently the burner/program doesn't like loading the file through my SIO2PC set-up. I tried two different eproms to make sure it wasn't the eprom, but both still tested empty after my burn attempts. So tonight I will transfer roms to burn to a real floppy and try again. So the hardware work will wait for another day.

Edited September 1, 2019 by Gunstar