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LDB (Super FX): Difference between revisions
From SnesLab
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|[[Sign Flag|S]] | |[[Sign Flag|S]] | ||
|[[CY]] | |[[CY]] | ||
|Z | |[[Zero Flag|Z]] | ||
|+ | |+ | ||
|0 | |0 | ||
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Part of the reason why LDB takes so many cycles is that the GSU waits for data to be loaded from game pak ram. | Part of the reason why LDB takes so many cycles is that the GSU waits for data to be loaded from game pak ram. | ||
The [[ALT0]] state is restored. | |||
The destination register should be specified in advance using [[WITH]] or [[TO]]. Otherwise, R<sub>0</sub> serves as the default. | The destination register should be specified in advance using [[WITH]] or [[TO]]. Otherwise, R<sub>0</sub> serves as the default. | ||
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=== See Also === | === See Also === | ||
* [[LDW]] | * [[LDW]] | ||
* [[STB]] | |||
* [[RAMB]] | * [[RAMB]] | ||
* [[ALT1]] | * [[ALT1]] | ||
Latest revision as of 05:20, 16 July 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | ROM Speed | RAM Speed | Cache Speed | ||
| Implied Indirect | 3D4m | 2 byte | 11 cycles | 13 cycles | 6 cycle | ||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| B | ALT1 | ALT2 | O/V | S | CY | Z | ||
| 0 | 0 | 0 | . | . | . | . | ||
LDB (Load Byte) is a Super FX instruction that loads one byte from the Game Pak and stores it in the low byte of the destination register. The high byte of the destination register is zeroed.
Part of the reason why LDB takes so many cycles is that the GSU waits for data to be loaded from game pak ram.
The ALT0 state is restored.
The destination register should be specified in advance using WITH or TO. Otherwise, R0 serves as the default.
Syntax
LDB (Rm)
where m can be from 0~11
Example
Let:
Dreg : R7 R1 = 3482h RAMBR : 70h (70:3482h) = 51h
After LDB (R1) is executed:
R7 = 0051h
See Also
External Links
- Official Super Nintendo development manual on LDB: 9.45 on Page 2-9-64 of Book II
- example: Page 2-9-65, lbid.