The ultimate UltiMax cartridge

From: Michał Pleban <>
Date: Tue, 22 Oct 2013 10:47:25 +0200
Message-ID: <>

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.


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Received on 2013-10-22 09:00:03

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