Date   : Mon, 13 Apr 2015 21:51:00 +0100 (WET-DST)
From   : bbcmicro@... (Peter Coghlan)
Subject: EPROM versus ROM for BBC/B OS1.2

>
> Can I use an EPROM instead of ROM in my BBC-B?
>

That should work.

>
> I tried to program an EPROM with OS1.2 but it didn't work.
> Why didn't it work??
>

Wrong type of EPROM?
Faulty EPROM?
EPROM not properly erased before programming?
EPROM not correctly programmed?
EPROM not correctly inserted in correct location?
Jumpers set for four 4K OS EPROMs instead of one 16K EPROM?
Some incompatibility between the hardware and OS1.2?

A 27128 EPROM should be suitable.  I vaguely recall reading that a 250ns part
is supposed to be required but don't quote me on that.  I think I've even had
success with 350ns parts in the paged ROM locations at least.  It should be
possible to get various other types of EPROM to work by suitable trickery.

If you post more details, it may be possible to provide more detailed help.
Eg, why you want to replace your OS, whether the machine worked before you
made changes to it, whether it works again now if you reverse the changes and
what exactly you mean by "didn't work" - does the machine just beep continuously
and show a blank screen when you power it up or does it just show the wrong
colours in MODE 2 or something else in between those two extremes?

What do you get on the screen, what state are the keyboard LEDs in and can you
get them to change state using the caps lock and shift lock keys?

Regards,
Peter Coghlan.