C8051F50x-F51x
SFR Page 0x0
Automatically
pushed on stack in
SFRPAGE on PCA
interrupt
0x0
SFRPAGE
SFRNEXT
SFRLAST
(PCA)
0xC
SFRPAGE
pushed to
SFRNEXT
(CAN0)
0x0
SFRNEXT
pushed to
SFRLAST
(SPI0DAT)
Figure 13.4. SFR Page Stack Upon PCA Interrupt Occurring During a CAN0 ISR
On exit from the PCA interrupt service routine, the CIP-51 will return to the CAN0 ISR. On execution of the
RETI instruction, SFR Page 0x00 used to access the PCA registers will be automatically popped off of the
SFR Page Stack, and the contents of the SFRNEXT register will be moved to the SFRPAGE register. Soft-
ware in the CAN0 ISR can continue to access SFRs as it did prior to the PCA interrupt. Likewise, the con-
tents of SFRLAST are moved to the SFRNEXT register. Recall this was the SFR Page value 0x00 being
used to access SPI0DAT before the CAN0 interrupt occurred. See Figure 13.5.
104
Rev. 1.1
SILICON [ SILICON ]
