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JohnBHanson · 13th Sep 2017, 11:46 pm

6802 is a 6800 but accepts a single phase clock (xtal).

On start up it reads the two bytes at the top of memory (locations 0xfffe and 0xffff)
and these are loaded into the program counter.

Note 0xfffe contains the most significant byte, oxffff contains the least significant byte

it will then start executing code at the program counter (interrupts are disabled at
that point).

NMI is by definition always enabled. It could be that the 6802 is getting an NMI
and that is causing the crash - worth a check.

I have had a quick scan of the instruction set and I don't think the CPU can issue a reset onto the bus - something else must be triggering the reset.

It could be that an external watchdog has been fitted and this is hitting the reset.

13th Sep 2017, 11:46 pm	#12
JohnBHanson Heptode Join Date: Aug 2009 Location: Worthing, Sussex, UK. Posts: 661	Re: Help with 6802 Microcontroller 6802 is a 6800 but accepts a single phase clock (xtal). On start up it reads the two bytes at the top of memory (locations 0xfffe and 0xffff) and these are loaded into the program counter. Note 0xfffe contains the most significant byte, oxffff contains the least significant byte it will then start executing code at the program counter (interrupts are disabled at that point). NMI is by definition always enabled. It could be that the 6802 is getting an NMI and that is causing the crash - worth a check. I have had a quick scan of the instruction set and I don't think the CPU can issue a reset onto the bus - something else must be triggering the reset. It could be that an external watchdog has been fitted and this is hitting the reset.