Help to program 16 bit EPROMs on a 8 bit programmer

Discuss hardware-related topics, such as development cartridges, CopyNES, PowerPak, EPROMs, or whatever.

Moderators: B00daW, Moderators

Post Reply
User avatar
Fisher
Posts: 1178
Joined: Sat Jul 04, 2015 9:58 am
Location: -29.794229 -55.795374

Help to program 16 bit EPROMs on a 8 bit programmer

Post by Fisher »

Hi.
I've been trying to program 16-bit EPROMs, but my programmer only supports the 8-bit ones.
It's a Genius G540.
I tried to find some kind of updated software that could support at least a 27c4100 with no luck.

I tried to use an SNES DIY game PCB to do the work:
Botton
Botton
Top
Top
So far so good, I was able to successfully read a Sonic 2 ROM:
Read results
Read results
Unfortunately, I can't program using this adapter.
Changing the pull-up resistor networks to pull down resulted in the EPROM being all 00's, which probably means that the programming sequence is doing well.
Maybe the multiplexers I'm using, 74HC257 aren't bi-directional, are they?
The datasheet says nothing about that...
Does such multiplex exist?

Another idea I had was to use a couple of 74HC245 bus transceivers.
If I do this, should one get the regular A0 signal and the other an inverted one?
What about the DIR pin?
Should I add a 78L05 to the VPP pin to select the direction or there's some better way to do it?

Thanks in advance.
lidnariq
Posts: 10712
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Help to program 16 bit EPROMs on a 8 bit programmer

Post by lidnariq »

Fisher wrote: Thu Jan 13, 2022 4:39 am Maybe the multiplexers I'm using, 74HC257 aren't bi-directional, are they?
Correct.
Does such multiplex exist?
Yes, an analog multiplexer such as the 74'3257, 4053, or 4551.
Should I add a 78L05 to the VPP pin to select the direction or there's some better way to do it?
Normal voltage regulators won't work with only 1.5V of headroom during programming, let alone when it's in verification mode and the programmer only provides 5V in the first place. Better to find a part (4000 series?) that can operate at 6.5V.
User avatar
TmEE
Posts: 796
Joined: Wed Feb 13, 2008 9:10 am
Location: Estonia, Rapla city (50 and 60Hz compatible :P)
Contact:

Re: Help to program 16 bit EPROMs on a 8 bit programmer

Post by TmEE »

Usually there's a byte mode on 16bit EPROMs, that will allow you to read/write everything with only 8 bit databus.
User avatar
Fisher
Posts: 1178
Joined: Sat Jul 04, 2015 9:58 am
Location: -29.794229 -55.795374

Re: Help to program 16 bit EPROMs on a 8 bit programmer

Post by Fisher »

That's an interesting information.
Unfourtunatelly, if I've read the datasheet correctly, it seems that the /BYTE pin is also the VPP pin.
Unless there's a trick that I didn't figure out yet I'm busted. :cry:
The EPROM is a ST 27c800.
User avatar
TmEE
Posts: 796
Joined: Wed Feb 13, 2008 9:10 am
Location: Estonia, Rapla city (50 and 60Hz compatible :P)
Contact:

Re: Help to program 16 bit EPROMs on a 8 bit programmer

Post by TmEE »

Ok, that prevents this idea...

But you can still program the chip one half at a time. Erase turns zeros into ones, and programming operation turn a one back to zero... so you can tie one byte high, while you program the other and do things in two passes.
User avatar
Fisher
Posts: 1178
Joined: Sat Jul 04, 2015 9:58 am
Location: -29.794229 -55.795374

Re: Help to program 16 bit EPROMs on a 8 bit programmer

Post by Fisher »

That's a nice Idea.
I think I have floating around an old MegaDrive GameGenie PCB.
Maybe just putting connectors where the old 8-bit ROMs are may do the trick.
I just need to remember where did I left it if it still exists in some way. :|
Post Reply