LS1 Lean Cruise

[rrauscher at nni.com]

No problem. . . (This is from memory as I do not have
my notes here). If you can refer to the '746 schematics,
it will help in following this.

The onboard ROM is disabled by tying the ROMEN line low.
A wire on one of the RomI/O chips does this (U7-1 to U7-22).

Locate the 74ls138 decoder chip (U8). This is the one that has
the chip select (CS) lines to the eprom & adc.

Move the ADC address from 0xC000 to 0xA000, this is a single
cut and jumper (pin 11 to pin 13). This will also need to be
changed in the code at three locations (no big deal, we have
access to it now!).

Now the address block from 0xC000 through 0xFFFF inclusive
is open. In this area a 128kb eprom can be used. The tricky
part is creating the proper CS signal. I used a 74ls00 piggy-
backed on top of the 74ls138 decoder already on board. Note
that the eprom CS is at 0xD000 of that decoder. Wire address
lines A14 & A15 to the 74ls00, use the output of the 74ls00 as
the new eprom CS. All these signals are available at the above
mentioned decoder.

Basically, the eprom is selected whenever address lines
a14 & a15 are both active (high).

Now expand the 24 pin eprom socket to 28 pins. I did this
by putting a 24 pin socket in the board, then a 28 pin socket
into that one. This allows access to the extra pins. Pin 24
of the orig eprom needs to be accessed also. This is vcc and
requires being moved to pin 28 of the new eprom. (Cut pin 24
out of the 24pin socket before soldering to board).

Two additional address lines added to the new eprom and the
hardware is done. These address lines are available locally
as they go to the service port.

Now the area from 0xC000 to 0xCFFF is all new eprom space,
with the original eprom code at 0xD000 and the original
rom code occupying the eprom from 0xE000-0xFFFF.

Use RTV to glue extra chips and wires in place for reliability.

BobR.


>
>OK, splill the beans what is going on here! <g>..
>This would have to work for the whole C3 series, No?.
>Bruce
>   AND the GUYS
>
>
> 
>> For those that are ok with a soldering iron, the best thing I
>> did was to put all of the code in the eprom. Even end up with
>> another 4Kb of space. . .
>> BobR.
>
>
>----------------------------------------------------------------------------


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