Re: Lisas and Modification

The screen modification kit includes the two CPU EPROMS, a Video State Machine bipolar PROM, and an inline autotransformer to modify the horizontal deflection.

Each Lisa's VSM PROM contains a unique serial number, which is read from the video data stream, then used to copy protect Lisa software.

The Screen Modification kit VSM PROM does not contain a valid serial number, so the Lisa O/S generates an error when you try to run it.

I suppose that it would have been possible to modify the CPU ROMs to read a serial number from the different video format to allow the OS to boot, however there may have been software already in circulation that used its own routines to verify the serial number, and it would fail.

There is also the logistical problem of how to program all those unique ROMS so that those who upgrade can still use the Lisa software which has already had the original serial number written to the floppy. This would have required all Apple dealers to have a PROM burner, or special order each PROM.

HTH James

>Unfortunately, Leo that is correct...maybe someone can give us the technical
>reason why. I know the kit includes the AB roms and I think a mod to the
>video board. Not sure which one of these is the culprit. The mac roms give
>a square screen aspect ratio where the Lisa roms are rectangular. But since
>the Lisa can operate in mac mode I don't know why the other way does not
>work. Maybe the video mod? I'd be interested in knowing...

>-----Original Message-----
>So a Lisa with the screen kit will NOT be able to run LisaOS?

James MacPhail                   "Think not of engineering as art,
uo957_at_email.domain.hidden                 but of art as engineering"
Sigma Seven Systems Ltd.
james_at_email.domain.hidden        <http://SigmaSevenSystems.com>

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