6502 BRK instruction

#1 · August 19, 2025, 5:28 pm

Hi all,

I think I found a bug. the BRK command should set the processor statusbit B to 1.

https://www.masswerk.at/6502/6502_instruction_set.html#BRK

I made a ben eater with a very little program. The B-Bit in the register is always 0.

Thanks.

Uploaded files:

hello-world-final.zip

#2 · August 19, 2025, 7:55 pm

Hi.

For me the he B flag is set to 1 when executing BRK.
Indeed I found that it is not cleared for NMI or IRQ, which is an error.
I mean the value pushed to STACK, the value in the actual status register is always 1.

Can you explain how do you see B flag is not set?

#3 · August 20, 2025, 2:54 pm

Although I mixed up the 1 and zero's in the mcu monitor processor status. I think you fixed the bug I encountered :). Thanks.

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