Datasheet

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PUSH SP

The stack pointer is changed after

a PUSH SP instruction.

POP SP

The stack pointer is not changed after a POP SP

instruction. The POP SP instruction places SP1 into the

stack pointer SP (SP2=SP1)

0xxxh

0xxxh − 2

0xxxh − 4

0xxxh − 6

0xxxh − 8

0123h

PUSH #0123h

POP R8Address

0123h

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CPU Registers

The PC can be addressed with all instructions and addressing modes. A few examples:

MOV #LABEL,PC ; Branch to address LABEL

MOV LABEL,PC ; Branch to address contained in LABEL

MOV @R14,PC ; Branch indirect to address in R14

3.2.2 Stack Pointer (SP)

The stack pointer (SP/R1) is used by the CPU to store the return addresses of subroutine calls and

interrupts. It uses a predecrement, postincrement scheme. In addition, the SP can be used by software

with all instructions and addressing modes. Figure 3-3 shows the SP. The SP is initialized into RAM by the

user, and is aligned to even addresses.

Figure 3-4 shows stack usage.

Figure 3-3. Stack Counter

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Stack Pointer Bits 15 to 1 0

MOV 2(SP),R6 ; Item I2 -> R6

MOV R7,0(SP) ; Overwrite TOS with R7

PUSH #0123h ; Put 0123h onto TOS

POP R8 ; R8 = 0123h

Figure 3-4. Stack Usage

The special cases of using the SP as an argument to the PUSH and POP instructions are described and

shown in Figure 3-5.

Figure 3-5. PUSH SP - POP SP Sequence

3.2.3 Status Register (SR)

The status register (SR/R2), used as a source or destination register, can be used in the register mode

only addressed with word instructions. The remaining combinations of addressing modes are used to

support the constant generator. Figure 3-6 shows the SR bits.

SLAU144J–December 2004–Revised July 2013 CPU

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