6502 brk instruction
What is the difference between BRK and 6502?
Instructions with functional differences The BRK instruction is the only instruction on the 65C02 that has a functional difference from the 6502, but the same cycle count. The IRQ, NMI, and RESET hardware interrupts have the same functional difference (and like BRK, an unchanged cycle count), which is covered below.
How does the 6502 handle BRK IRQ NMI & reset?
One interesting thing here is the question how the 6502 handles BRK, IRQ, NMI and RESET. Let’s revisit the documented part first. The 6502 knows three vectors at the top of its address space: On a RESET, the CPU loads the vector from $FFFC/$FFFD into the program counter and continues fetching instructions from there.
How many cycles does a 6502 take?
On the 6502, these four instructions always take 7 cycles, regardless of whether a page boundary was crossed or not. On the 65C02, they take 6 cycles when a page boundary is not crossed, and take 7 cycles when a page boundary is crossed. The instructions are otherwise the same on the 6502 and 65C02.
Is the 6502 read-only?
Elaborating further: the 6502 will have been in read-only mode since during the T0 SD1 cycle, which is the cycle after the sense cycle.
The Specification
Let’s revisit the documented part first. The 6502 knows three vectors at the top of its address space: 1. On a RESET, the CPU loads the vector from $FFFC/$FFFD into the program counter and continues fetching instructions from there. 2. On an NMI, the CPU pushes the low byte and the high byte of the program counter as well as the processor status on
Brk
Ignoring opcode fetches, the PLA ROM defines the following cycles of the BRK instruction (6502 Programming Manual, page 131): 1. store PC(hi) 2. store PC(lo) 3. store P 4. fetch PC(lo) from $FFFE 5. fetch PC(hi) from $FFFF pagetable.com
Irq
An IRQ does basically the same thing as a BRK, but it clears the B flag in the pushed status byte. The CPU goes through the same sequence of cycles as in the BRK case, which is done like this: If there is an IRQ pending and the current instruction has just finished, the interrupt logic in the 6502 forces the instruction register (“IR”) to “0”, so i
Nmi
Not surprisingly, NMI is done the same way: “0” is injected into the instruction stream, but this time, some extra logic makes sure that the addresses $FFFA/$FFFB are put onto the address bus when fetching the vector. pagetable.com
Reset
RESET also runs through the same sequence, but it is the most different of the four cases, since it does not write the current PC and status onto the stack – but this was hacked trivially: The bus cycles exist, but the read/write line is not set to “write”, but “read” instead. The following trace was created with the transistor data from the Visual
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6502 Interrupt and Bus
Software Interrupt: caused by BRK instruction (sets break flag). • Interrupt call pushes status register to stack. • Detect what kind of interrupt. |
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OpenCores 6502 IP Core Specification
15 sept. 2018 R6502 IP Core ... Figure (2): R6502_TC IP core architecture . ... If an NMI occurred after a BRK instruction was fetched and before the ... |
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W65C02S 8–bit Microprocessor
8 avr. 2022 The BRK instruction for both the NMOS 6502 and 65C02 is a 2 byte instruction. The NMOS and CMOS devices simply skips the second byte (i.e. ... |
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W65C02S 8–bit Microprocessor
8 oct. 2018 Instructions obtained from program memory are executed by ... The BRK instruction for both the NMOS 6502 and 65C02 is a 2 byte instruction. |
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MOS Technology 6502 CPU Emulation
1 mai 2020 One of these is referred to as The B Flag and is set if the. BRK (Break) instruction has been executed. The last bit is simply unused with no ... |
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KIM Uno Manual v2.pdf
Simple: enter value 00 (for the 6502's BRK instruction) in the address you want to generate a break point at. Do not forget to note down the. |
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6502alan instruction set
6502alan Machine Language Instruction Set. © 2008-2014 Alan G. Labouseur alan@Labouseur.com Break (which is really a system call) 00 BRK 00. |
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6502-6809 TRANSLATOR - by Edgar M. (Bud) Pass Ph.D
The 6502 BRK instruction has no exact 6809 counterpart with respect to the "B" flag in the condition code register. However if 6502 stack emulation and |
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R65C02 R65C102 and R65C112 R65C00 Microprocessors (CPU)
Pin compatible with NMOS R6502 (2) R6502 instruction with additional addressing mode(s). ... BRK. O? Implied. 1 7. R65C00 Microprocessors (CPU). |
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KRUSADER
when the 6502 executes a BRK instruction the return address pushed onto the stack is PC+2 |
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6502 Interrupt and Bus - JHU Computer Science
Software Interrupt: caused by BRK instruction (sets break flag) • Interrupt call pushes status register to stack • Detect what kind of interrupt Address Bytes |
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20 Interrupts and Breaks
The IRQ has two instructions associated with it which directly affect bit 2 of the When the 6502 encounters a BRK instruction it does a number of things-in fact, |
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Advanced 6502 Assembly Language Programming on the Apple //e
6502 Instruction Encoding Useful in interrupt routines and returning from BRK BRK is a software interrupt that pushes the current program counter and |
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Programming the 65816 - 6502org
6502/65C02 Addressing Modes on the 65816 interrupts - which are caused by the execution of the break instruction (BRK) If any hardware can cause a |
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6502 Instructions
2-byte instruction, and none in a 1-byte Instruction APPLE ZERO-PAGE BRK BPL Rei CPX#lmm CPXZP CPX Abs BNERel CMP#lmm CMPZP CMPZP,X |
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The 6502 Instruction Set
SED Set decimal mode flag D SEI Set interrupt disable flag I Subroutine and Interrupt Group JSR Jump to a subroutine RTS Return from subroutine BRK |
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6502 Brk Instruction - WordPresscom
6502 Brk Instruction Despite what some 6502 references might appear to claim on a first reading, there Two interrupts (/IRQ and /NMI) and two instructions |
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6502 instructions - DigitalOcean
The “BIT” instruction of the 6502 has been created for this specific purpose 0081: C6 00 DEC T 0083: 10* El BPL SOUND 0085: 00 BRK SYMBOL T |
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The Visible Computer-6502 Manual
So far we know exactly two of the fifty-six 6502 instructions LDA, also known as $ A9: "load the accumulator with the byte following this one", and BRK, $00, |
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6502 - Description
Read/modify/write instructions at effective address Decimal flag Indeterminate after reset Flags after decimal operation Interrupt after fetch of BRK instruc |
