PIC18F2331 MICROCHIP [Microchip Technology], PIC18F2331 Datasheet - Page 61

• Manufacturer Part Number: PIC18F2331
• Description: 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D
• Manufacturer: MICROCHIP [Microchip Technology]

REGISTER 5-1:
5.2.3
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 cur-
rent 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.
 2003 Microchip Technology Inc.
bit 7
bit 6
bit 5
bit 4-0
PUSH AND POP INSTRUCTIONS
(1)
(1)
STKPTR REGISTER
bit 7
STKFUL: Stack Full Flag bit
1 = Stack became full or overflowed
0 = Stack has not become full or overflowed
STKUNF: Stack Underflow Flag bit
1 = Stack underflow occurred
0 = Stack underflow did not occur
Unimplemented: Read as ‘0’
SP4:SP0: Stack Pointer Location bits
Legend:
R = Readable bit
- n = Value at POR
STKFUL
R/C-0
Note 1: Bit 7 and bit 6 are cleared by user software or by a POR.
STKUNF
R/C-0
PIC18F2331/2431/4331/4431
W = Writable bit
‘1’ = Bit is set
U-0
Preliminary
—
R/W-0
SP4
5.2.4
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 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 POR Reset.
U = Unimplemented
‘0’ = Bit is cleared
R/W-0
SP3
STACK FULL/UNDERFLOW RESETS
R/W-0
SP2
C = Clearable only bit
x = Bit is unknown
R/W-0
SP1
DS39616B-page 59
R/W-0
SP0
bit 0