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Program Counter: Difference between revisions
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The '''Program Counter''' (PC) keeps track of which instruction is currently executing. If incremented past FFFFh, it wraps around to zero. | The '''Program Counter''' (PC) keeps track of which instruction is currently executing. If incremented past FFFFh, it wraps around to zero. | ||
The 6502 had 16-bit absolute addressing but only an 8-bit adder, so in [[emulation mode]] branches that cross a page boundary incur a one cycle penalty. | The 6502 had 16-bit absolute addressing but only an 8-bit adder, so in [[emulation mode]] branches that cross a page boundary incur a one cycle penalty. 65c816 native mode has no such penalty because the full 16-bit adder is used. | ||
On the [[S-SMP]] it is 16 bits wide. The low byte is called PCL and the high byte is called PCH. | On the [[S-SMP]] it is 16 bits wide. The low byte is called PCL and the high byte is called PCH. | ||
Revision as of 22:05, 22 July 2024
The Program Counter (PC) keeps track of which instruction is currently executing. If incremented past FFFFh, it wraps around to zero.
The 6502 had 16-bit absolute addressing but only an 8-bit adder, so in emulation mode branches that cross a page boundary incur a one cycle penalty. 65c816 native mode has no such penalty because the full 16-bit adder is used.
On the S-SMP it is 16 bits wide. The low byte is called PCL and the high byte is called PCH.
See Also
References
- Eyes & Lichty page 33, https://archive.org/details/0893037893ProgrammingThe65816/page/33
- subparagraph 8.1.4 on page 3-8-4 of Book I of the official Super Nintendo development manual
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#PC
- Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.2.1.1