Re: VIC-20 "all games in one" cartridge update

From: Marko Mäkelä (
Date: 2001-04-01 13:52:25

On Fri, 30 Mar 2001, john/lori wrote:

> Why 3.3 volts?
> Is there some good reason for that (the ROM only comes in an LV version
> or something)?

Yes, the Am29LV160 boot-sector flash ROM is only available as a
low-voltage version.  If you know of a programmable ROM that is available
in an SMD package and has at least 2 megabytes of capacity, please let me
know.  Other chips could be powered from 5 volts.

> Presummably the 74LVX245 does the level translation, but 74LVX__
> aren't dual supply are they? (the 74LVX__ are 5V tolerant in, but
> isn't there some other family for driving 5V?)

The ON Semiconductors (former Motorola) 74LVX245 data sheet, page 1
<URL:> mentions
something about "a parasitic diode" being formed between the bus and Vcc
terminals.  I don't know if this is a problem; aren't there some internal
NMOS pullups on the data bus?  According to the schematic diagram
251027-01 sheet 1, left side, the data bus on the cartridge port is wired
directly to the 6502 and to a 74LS245 in the VIC-20.

I managed to reduce the number of vias to 25 (not bad, since 19 signals
need to be routed from one side to another).  The board is now about 53 mm
tall.  Three boards could be fitted on a standard 160 by 100 mm circuit
board.  By making photo masks of exactly that size, it should be possible
to align the bottom and top sides without special equipment.  And there's
no need to drill any holes, since all chips are SMD.  Just solder wires
around the edge of the card.  No vias are located under any chip.


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