C8051F54X_14 Datasheet, PDF (95/275 Pages) Silicon Laboratories – Mixed Signal ISP Flash MCU Family

SFRNEXT
popped to
SFRPAGE
SFR Page 0x00
Automatically
popped off of the
stack on return from
interrupt
0x0F
(SMB0ADR)
C8051F54x
SFRPAGE
SFRNEXT
SFRLAST
Figure 12.6. SFR Page Stack Upon Return From SPI0 Interrupt
In the example above, all three bytes in the SFR Page Stack are accessible via the SFRPAGE, SFRNEXT,
and SFRLAST special function registers. If the stack is altered while servicing an interrupt, it is possible to
return to a different SFR Page upon interrupt exit than selected prior to the interrupt call. Direct access to
the SFR Page stack can be useful to enable real-time operating systems to control and manage context
switching between multiple tasks.
Push operations on the SFR Page Stack only occur on interrupt service, and pop operations only occur on
interrupt exit (execution on the RETI instruction). The automatic switching of the SFRPAGE and operation
of the SFR Page Stack as described above can be disabled in software by clearing the SFR Automatic
Page Enable Bit (SFRPGEN) in the SFR Page Control Register (SFR0CN). See SFR Definition 12.1.
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