7.5 Automatic Context Saving

Upon entering an interrupt, the return PC address is saved on the stack. Additionally, the following registers are automatically saved in the shadow registers:
  • W register
  • STATUS register (except for TO and PD)
  • BSR register
  • FSR registers
  • PCLATH register

Upon exiting the Interrupt Service Routine, these registers are automatically restored. Any modifications to these registers during the ISR will be lost. If modifications to any of these registers are desired, the corresponding shadow register may be modified and the value will be restored when exiting the ISR. The shadow registers are available in Bank 63 and are readable and writable. Depending on the user’s application, other registers may also need to be saved.