Stack Pointer

The CPU.SP register holds the Stack Pointer (SP) that points to the top of the stack. After being reset, the SP points to the highest internal SRAM address.

Only the number of bits required to address the available SRAM is implemented for each device. The remaining bits are set, so the Stack Pointer (SP) always points to the SRAM.

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.

To prevent corruption when updating the SP from software, a write to CPU.SPL will automatically disable interrupts for the following four instructions or until the next I/O memory write, whichever comes first.

Name:
SP
Offset:
0x0D
Reset:
Top of stack
Access:
-
Bit15141312111098
SP[15:8]
AccessR/WR/WR/WR/WR/WR/WR/WR/W
Reset
Bit76543210
SP[7:0]
AccessR/WR/WR/WR/WR/WR/WR/WR/W
Reset

Bits 15:8 – SP[15:8]: Stack Pointer High Byte

Stack Pointer High Byte

These bits hold the MSB of the 16-bit register.

Bits 7:0 – SP[7:0]: Stack Pointer Low Byte

Stack Pointer Low Byte

These bits hold the LSB of the 16-bit register.