Every function does not cause a problem. The main line code context uses the Register set 0 exclusively. All interrupt routines in my application are tagged with "USING 1". All subroutines called by the interrupt routines are tagged with "USING 1". In general it is not a good idea to tag just run of the mill subroutines with the USING attribute.

Actually with the Keil scheme that I showed before the F1 flag is actually working in the application as long as all interrupt priorities are kept at the default low priority setting. The fact that the application is in its ISR means that my switcher code has already done its thing, and they do restore the original contents of the PSW at the end of the application interrupt routine.

The problem I have with the Keil hard setting a value into the PSW to set the register banks of the interrupt routines comes into play with the use of prioritized interrupts. In this case a higher priority one can interrupt a low priority interrupt already in process. If one of the shared interrupts is one of those of the higher priority then it gets blown out of the water whenever the Keil method of implementing the RS0/RS1 bits casues the F1 and F0 flags to change value becasue they choose to load PSW with an immediate value.

Michael Karas