6502Observations

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Notes here on bugs and undocumented behaviour.
Notes here on bugs and undocumented behaviour.
* [[6502_BRK_and_B_bit|BRK, the B bit]], and other interrupts
* [[6502_BRK_and_B_bit|BRK, the B bit]], and other interrupts
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* [[6502_Taken_Branch_Delays_Interrupts|Branches and interrupts]] whereby a taken branch delays interrupt handling
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* [[6502 Timing of Interrupt Handling|Timing of Interrupt Handling]] noting that a taken branch delays interrupt handling, also that CLI/PLP allow one further instruction to execute, unlike RTI.
* [[6502_Unsupported_Opcodes|Unsupported or undocumented opcodes]] such as SAX and XAA
* [[6502_Unsupported_Opcodes|Unsupported or undocumented opcodes]] such as SAX and XAA
* [[6502_ROR_bug|The ROR bug]] which is found only in rare early devices
* [[6502_ROR_bug|The ROR bug]] which is found only in rare early devices

Latest revision as of 08:14, 16 May 2011

We've found some interesting things on the 6502, from the layout level, up through circuit level to the programmer visible level.

Programmer Visible

Notes here on bugs and undocumented behaviour.

See also our catalogue of 6502 test programs, useful to verify simulators or emulators.

Circuit and Logic

Notes here on timing fixes and non-digital circuit techniques, and departures from NMOS design style orthodoxy.

Layout

Notes here on the traces of bug fixes, and remnants of the original 6501 layout.

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