8.7.2 Stack Pointer
The CPU.SP holds the Stack Pointer (SP) that points to the top of the Stack. After Reset, the Stack Pointer points to the highest internal SRAM address.
Only the number of bits required to address the available data memory including external memory (up to 64KB) is implemented for each device. Unused bits will always read as zero.
The CPU.SPL and CPU.SPH register pair represents the 16-bit value, CPU.SP. The low byte [7:0] (suffix L) is accessible at the original offset. The high byte [15:8] (suffix H) can be accessed at offset + 0x01. For more details on reading and writing 16-bit registers, refer to 8.5.6 Accessing 16-bit Registers.
To prevent corruption when updating the Stack Pointer from software, a write to CPU.SPL will automatically disable interrupts for the next four instructions or until the next I/O memory write.
| Name: | SP |
| Offset: | 0x0D |
| Reset: | 0xxxxx |
| Property: | - |
| Bit | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | |
| SP[15:8] | |||||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W | |
| Reset | x | x | x | x | x | x | x | x | |
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
| SP[7:0] | |||||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W | |
| Reset | x | x | x | x | x | x | x | x | |
Bits 15:8 – SP[15:8] Stack Pointer high byte
These bits hold the MSB of the 16-bit register.
Bits 7:0 – SP[7:0] Stack Pointer low byte
These bits hold the LSB of the 16-bit register.