[Tech] Double rom thing again

[guddler]

[ukvac] [Tech] Double rom thing again
You can tell i've been away all weekend :O)

Back to having double size roms. The game in question has an unused dip
switch. Is there a single line coming off the Z80 or Z80's that hold the
address that is to be read from the EPROMs?

If so, could i not run an output from the dip, together with the address
from the CPU to a NAND(?) gate so the addres bit never gets messed with if
the dip is off and the bit is always inverted in any other combination (ie,
the dip is on)?

Or again, am i just daydreaming?

Martin.

---------------------------------------------------
Martin White

Coming real soon...
http://www.guddler.btinternet.co.uk

Yet another arcade site(!) with info on games owned, repair logs (as and
when), projects and more.



Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

 

[MrMish]

Re: [ukvac] [Tech] Double rom thing again
> Back to having double size roms. The game in question has an unused dip
> switch. Is there a single line coming off the Z80 or Z80's that hold the
> address that is to be read from the EPROMs?
The program rom in Mr Do runs from 0 to 0x7fff in the z80 address
space. So if you wanted to know whether the game was accessing the rom,
you could take (NOT A15) from the z80 address bus.

> If so, could i not run an output from the dip, together with the address
> from the CPU to a NAND(?) gate so the addres bit never gets messed with if
> the dip is off and the bit is always inverted in any other combination (ie,
> the dip is on)?
Mmm, don't see why not. Presumably you are going to run that line to
the top address lines of the program eproms? That will allow program
switching, but not graphics roms. In fact I don't believe the graphics
roms are accessed at all by the Z80, as far as I know the z80 only see's
the program, and the graphics eproms are on a different bus connected to
the graphics hardware only. The z80 & graphics just communicate through
some ram.

Bryan



Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/