Re: The ultimate UltiMax cartridge

Hi Michau, cool progress. A couple of questions/observations.

I assume you mean /EXRAM and not /EXROM?

Did you determine whether your MAX machine matches the schematic from 
Ruud or the reversed engineered one from Donato Travaglini? The ones 
that Steve and I have match the latter and for those, pins 9 & 10 must 
be jumpered for the CIA to get it's select signal.

How will you initialise the latch when you power on? In my prototype I 
used a 74LS174 which is a hex latch with a master clear tied to the 
reset line. This way bank 0 of the EPROM is always going to be selected 
at reset and it meant I have a reset button which always takes me back 
to the image selection menu.

I guess I should get on with finishing the boot menu and ROM image!

cheers,

Rob


On 22/10/2013 10:47, Michał Pleban wrote:
> Hello!
> 
> Yesterday I was on a 8 hour train journey, so to kill time I designed
> the UltiMax cartridge and laid out a PCB for it. It looks like
> everything just fit on the cartridge PCB I got from Ruud.
> 
> Here's how it is supposed to work. Sorry I don't have a schematic yet;
> generally I don't believe in schematics and I always lay PCBs without
> one. Maybe on a next train journey I'll have time to draw it :-) But
> here's what I got on the PCB:
> 
> * A 27C801 EPROM.
> * A 6116 SRAM.
> * All needed address and data lines connected properly to these.
> * A 74LS273 resettable latch, with outputs Q0-Q5 going to high address
> lines of the EPROM, and Q7 used as below.
> * A 74LS08 and 74LS04 for glue logic.
> 
> The idea is that initially, the latch sits at the /EXROM line. This is
> done as follows:
> 
> 74LS273.CLK = /EXROM & 74LS273.Q7
> 
> So as long as we write values to the latch with it 7 set to 0, the 
> latch
> still operates. But if we set bit 7 to 1, the latch becomes inactive. 
> In
> such case, the RAM will become active, because:
> 
> 6116.CS = /EXROM & ! 74LS273.Q7
> 
> So to enable a cartridge, we write correct bank number to the latch 
> ORed
> with $80. The latch disappears and the RAM takes its place.
> 
> Of course, there are some other needed signals:
> 
> 27C801.CS = /ROMH & /ROML
> 27C801.A13 = /ROML
> 27C801.OE = 6116.OE = ! RW
> 6116.WE = RW
> 
> I need to verify the PCB now and I will send it for prototype 
> production.
> 
> Regards,
> Michau.
> 
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