Hardware processing continues with the hardware restoration of the PC and the PSW from the stack. This portion takes 6 clocks. This is pretty efficient, but what if one could cut out the pushing and popping of the PSW and PC? Well, one can with the RX Fast Interrupt. The user can specify one interrupt source as the Fast Interrupt. The Fast Interrupt differs from other interrupts in that the PC and PSW, instead of being stored on the stack, are stored in dedicated backup registers which are much faster to access. So the hardware portion of the context save and restore are sped up. Here is what it looks like… When the interrupt fires now the PC and PSW are stored in the backup registers. This saves 2 clocks on entry. As before, software saves additional registers on entry to the ISR, executes the ISR code and then restores registers on exit.