[Coco] 6309 bitmd instruction
boisy at boisypitre.com
Sun Feb 19 14:40:35 EST 2006
Never mind about this post. I just read the 6309 secret features
memo, which details why I am not seeing the Z flag of CC set:
3. The MD register
This is a 8 bit register to keep the mode and status of the chip.
The meaning of each bit is as follow.
bit 7 --- 1 is set if zero division happen.
bit 6 --- 1 is set if illegal instruction is fetched.
bit 1 --- The mode for FIRQ interrupt.
0 -> the the action for FIRQ is the same as that
1 -> the the action for FIRQ is the same as IRQ.
bit 0 --- The execution mode of 6309.
0 -> the emulation mode.
1 -> the native mode.
(When the chip is reseted, all bits are 0.)
So it appears that bits 0 and 1 are write only.
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