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Program Counter Relative Addressing: Difference between revisions
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'''Program Counter Relative Addressing''' is supported by nine instructions on the [[65c816]]: | |||
* [[BCC]] (opcode 90) | |||
* [[BCS]] (opcode B0) | |||
* [[BEQ]] (opcode F0) | |||
* [[BMI]] (opcode 30) | |||
* [[BNE]] (opcode D0) | |||
* [[BPL]] (opcode 10) | |||
* [[BRA]] (opcode 80) | |||
* [[BVC]] (opcode 50) | |||
* [[BVS]] (opcode 70) | |||
All of which are two bytes long. | |||
The '''effective address''' is generated by sign-extending the 8-bit operand to 16 bits and then adding it to the [[program counter]]. The [[program bank register]] remains the same. | |||
==== Syntax ==== | |||
<pre> | |||
BRA nearlabel | |||
</pre> | |||
Where nearlabel is in the range of -128 to 127 bytes away from the next opcode after BRA. | |||
=== See Also === | |||
* [[Program Counter Relative Long Addressing]] | |||
=== References === | |||
* [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/399 page 399] | |||
* section 3.5.21 of 65c816 datasheet, https://westerndesigncenter.com/wdc/documentation/w65c816s.pdf | |||
* Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#5.18 | |||
[[Category:ASM]] | |||
[[Category:Addressing Modes]] | [[Category:Addressing Modes]] | ||
[[Category:Inherited from 6502]] | |||
Latest revision as of 04:44, 9 August 2024
Program Counter Relative Addressing is supported by nine instructions on the 65c816:
- BCC (opcode 90)
- BCS (opcode B0)
- BEQ (opcode F0)
- BMI (opcode 30)
- BNE (opcode D0)
- BPL (opcode 10)
- BRA (opcode 80)
- BVC (opcode 50)
- BVS (opcode 70)
All of which are two bytes long.
The effective address is generated by sign-extending the 8-bit operand to 16 bits and then adding it to the program counter. The program bank register remains the same.
Syntax
BRA nearlabel
Where nearlabel is in the range of -128 to 127 bytes away from the next opcode after BRA.
See Also
References
- Eyes & Lichty, page 399
- section 3.5.21 of 65c816 datasheet, https://westerndesigncenter.com/wdc/documentation/w65c816s.pdf
- Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#5.18