Stack Pointer: Difference between revisions

Revision as of 20:15, 12 November 2024

The Stack Pointer (SP) points to the next stack location available for pushing to. On the SPC700 it is 16-bit, but the upper byte is fixed by the hardware to be 0x01.

On the 65c816, the only two instructions that modify the stack pointer (S) directly are TCS and TXS.^[4] It is only fixed to be in page one in emulation mode on the '816.

1FFh is a common value to initialize the stack pointer to.

Pushing things onto the stack decrements the stack pointer and pulling things increments it.

References

subparagraph 8.1.5 of page 3-8-4 of Book I of the official Super Nintendo development manual
diversified activities: page 3-8-5 of Book I, lbid.
Eyes & Lichty, page 31 on The Stack Pointer
Eyes & Lichty, page 511 on TCS

@@ Line 1: / Line 1: @@
-The '''Stack Pointer''' (SP) on the [[SPC700]] is 16-bit, but the upper byte is fixed by the hardware to be 0x01.
+The '''Stack Pointer''' (SP) points to the next [[stack]] location available for pushing to.  On the [[SPC700]] it is 16-bit, but the upper byte is fixed by the hardware to be 0x01.
 On the [[65c816]], the only two instructions that modify the stack pointer (S) directly are [[TCS]] and [[TXS]].<sup>[4]</sup>  It is only fixed to be in page one in [[emulation mode]] on the '816.
@@ Line 5: / Line 5: @@
 FFh is a common value to initialize the stack pointer to.
-Pushing things onto the [[stack]] decrements the stack pointer and pulling things increments it.  It points to the next available location on the stack.
+Pushing things onto the [[stack]] decrements the stack pointer and pulling things increments it.
 === See Also ===