PIC18F2331_07 Datasheet, PDF (63/400 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D

PIC18F2331/2431/4331/4431
REGISTER 5-1: STKPTR: STACK POINTER REGISTER
R/C-0
R/C-0
U-0
STKFUL⁽¹⁾ STKUNF⁽¹⁾
—
bit 7
R/W-0
SP4
R/W-0
SP3
R/W-0
SP2
R/W-0
SP1
R/W-0
SP0
bit 0
Legend:
R = Readable bit
-n = Value at POR
C = Clearable-only bit
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
x = Bit is unknown
bit 7
bit 6
bit 5
bit 4-0
STKFUL: Stack Full Flag bit⁽¹⁾
1 = Stack became full or overflowed
0 = Stack has not become full or overflowed
STKUNF: Stack Underflow Flag bit⁽¹⁾
1 = Stack underflow occurred
0 = Stack underflow did not occur
Unimplemented: Read as ‘0’
SP4:SP0: Stack Pointer Location bits
Note 1: Bit 7 and bit 6 are cleared by user software or by a POR.
5.2.3 PUSH AND POP INSTRUCTIONS
Since the Top-of-Stack (TOS) is readable and writable,
the ability to push values onto the stack and pull values
off the stack without disturbing normal program execu-
tion is a desirable option. To push the current PC value
onto the stack, a PUSH instruction can be executed.
This will increment the Stack Pointer and load the
current PC value onto the stack. TOSU, TOSH and
TOSL can then be modified to place data or a return
address on the stack.
The ability to pull the TOS value off of the stack and
replace it with the value that was previously pushed
onto the stack, without disturbing normal execution, is
achieved by using the POP instruction. The POP instruc-
tion discards the current TOS by decrementing the
Stack Pointer. The previous value pushed onto the
stack then becomes the TOS value.
5.2.4 STACK FULL/UNDERFLOW RESETS
These Resets are enabled by programming the
STVREN bit in Configuration Register 4L. When the
STVREN bit is cleared, a full or underflow condition will
set the appropriate STKFUL or STKUNF bit, but not
cause a device Reset. When the STVREN bit is set, a
full or underflow condition will set the appropriate
STKFUL or STKUNF bit and then cause a device
Reset. The STKFUL or STKUNF bits are cleared by the
user software or a Power-on Reset.
© 2007 Microchip Technology Inc.
Preliminary
DS39616C-page 61