RE: BASIC and System ROM replacements

From: Baltissen, GJPAA (Ruud) <>
Date: Mon, 27 May 2013 10:20:40 +0000
Message-ID: <>
Hallo Micha, 

> Still it does not solve the problem of how to return to the
> previous bank after interrupt ...

I thought I mentioned a solution that can be used in an earlier email. 
Assume that the main bank contains the main interrupt routines. The interrupt vectors of the other banks point to a small routine. This small routine pushes A, Y and X, and then reads the bank register and pushes that as well. Next it JSRs to a routine in RAM that 1) switches to the main bank and 2) JSRs to the main interrupt routine. The main routine pushes the same value but can skip the RAM routine.

At the end the main routine a RTS will take care of returning to the RAM routine again. The RAM routine pulls the bank value, restores the bank and a RTS takes care of returning to the original interrupt routine. 

Another idea, but it will cost (just) a bit more RAM: let the vectors point directly to RAM and let the routine in RAM do the first four pushes, etc. etc. No small routines in the individual banks needed anymore.

Jut my two cents....

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Received on 2013-05-27 11:00:14

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