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Program Counter Relative Addressing: Difference between revisions

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'''Program Counter Relative Addressing''' is supported by nine instructions:
'''Program Counter Relative Addressing''' is supported by nine instructions on the [[65c816]]:


* [[BCC]] (opcode 90)
* [[BCC]] (opcode 90)
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All of which are two bytes long.
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 ====
==== Syntax ====
<pre>
<pre>
BRA label
BRA nearlabel
</pre>
</pre>
Where nearlabel is in the range of -128 to 127 bytes away from the next opcode after BRA.


=== See Also ===
=== See Also ===
* [[Program Counter Relative Long Addressing]]
* [[Program Counter Relative Long Addressing]]


=== Reference ===
=== References ===
* [[Eyes & Lichty]] page 399, https://archive.org/details/0893037893ProgrammingThe65816/page/399
* [[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
* 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:ASM]]
[[Category:Addressing Modes]]
[[Category:Addressing Modes]]
[[Category:Inherited from 6502]]
[[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