Date   : Thu, 03 Aug 2006 12:06:05
From   : "Steve O'Leary" <navalenigma@...>
Subject: Re: Electron cartridge interface

> Date: Thu, 3 Aug 2006 11:42:28 +0100
> From: hick.bbc@...
> To: bbc-micro@...
> Subject: Re: [BBC-Micro] Electron cartridge interface
> > On Thu, 3 Aug 2006, Steve O'Leary wrote:
> > > It's been a long time since I've looked at this and most of the 
> > connections are obvious but some could benefit from a description. For
> > example the ROM_OE which I would hazard a guess is the ROM Output Enable 
> > and this would go hi when the electron is wanting to page in a sideways 
> > ROM/RAM. But this is only a guess ?
> > It goes high  on a memory access to either valid ROM socket (0,1 or 2,3) 
> > for the slot.
> > (ROM)QA provides the low bit of the  ROM socket accessed.
> > There is also a select line for ROM socket 13, it's probably A19 
> > "reserved".

That's great it was mostly the ROM access I was interested in. I thought
that you could only access 2 roms per slot but couldn't see how they could
be selected, the QA solves this riddle. Are there any more connected with
sideways ROM/RAM access that I should be aware of (besides R/!W etc.)

What was special about ROM socket 13 that it was mapped to the cartridge
slot and how did this work if you had hardware in both cartridge slots
that looked at the ROM 13 line ? it couldn't use both ? Or was this
feature never implemented on this 'reserved' line.
 
Thanks for the help.
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