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TRB: Difference between revisions
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'''TRB''' (Test and Reset Bits) is a [[65c816]] instruction that tests and resets bits using the [[accumulator]]. For each set bit in the accumulator, the corresponding memory bit | '''TRB''' (Test and Reset Bits) is a [[65c816]] instruction that tests and resets bits using the [[accumulator]]. For each set bit in the accumulator, TRB clears the corresponding memory bit. | ||
TRB performs a logical AND (conjunction) and the [[zero flag]] is set or cleared to reflect whether the conjunction is zero. The conjunction itself is discarded. | TRB performs a logical AND (conjunction) and the [[zero flag]] is set or cleared to reflect whether the conjunction is zero. The conjunction itself is discarded. | ||
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==== Cycle Penalties ==== | |||
* In both [[addressing modes]], TRB takes two extra cycles if the accumulator is 16 bits wide. | * In both [[addressing modes]], TRB takes two extra cycles if the accumulator is 16 bits wide. | ||
* In [[direct page addressing]], TRB takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | * In [[direct page addressing]], TRB takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | ||
Latest revision as of 17:50, 23 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Absolute | 1C | 3 bytes | 6 cycles* | ||||
| Direct Page | 14 | 2 bytes | 5 cycles* | ||||
| Flags Affected | |||||||
|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C |
| . | . | . | . | . | . | Z | . |
TRB (Test and Reset Bits) is a 65c816 instruction that tests and resets bits using the accumulator. For each set bit in the accumulator, TRB clears the corresponding memory bit.
TRB performs a logical AND (conjunction) and the zero flag is set or cleared to reflect whether the conjunction is zero. The conjunction itself is discarded.
Syntax
TRB addr TRB dp
Cycle Penalties
- In both addressing modes, TRB takes two extra cycles if the accumulator is 16 bits wide.
- In direct page addressing, TRB takes another extra cycle if the low byte of the direct page register is nonzero.
See Also
External Links
- Eyes & Lichty, page 513 on TRB
- Labiak, page 194 on TRB
- snes9x implementation of TRB: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1338
- undisbeliever on TRB: https://undisbeliever.net/snesdev/65816-opcodes.html#trb-test-and-reset-memory-bits-against-accumulator]