C8051F54X_14 Datasheet, PDF (93/275 Pages) Silicon Laboratories – Mixed Signal ISP Flash MCU Family

C8051F54x
SFR Page 0x00
Automatically
pushed on stack in
SFRPAGE on PCA
interrupt
SFRPAGE
pushed to
SFRNEXT
SFRNEXT
pushed to
SFRLAST
0x00
(PCA0)
0x00
(SPI0)
0x0F
(SMB0ADR)
SFRPAGE
SFRNEXT
SFRLAST
Figure 12.4. SFR Page Stack Upon PCA Interrupt Occurring During a SPI0 ISR
On exit from the PCA interrupt service routine, the CIP-51 will return to the SPI0 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 SPI0 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 0x0F being
used to access SMB0ADR before the SPI0 interrupt occurred. See Figure 12.5.
Rev. 1.1
93