[Coco] 6309 bitmd instruction

Boisy Pitre 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.

      Read value
         bit 7  ---  1 is set if zero division happen.
         bit 6  ---  1 is set if illegal instruction is fetched.

      Write value
         bit 1  ---  The mode for FIRQ interrupt.
                     0 -> the the action for FIRQ is the same as that
                          of 6809.
                     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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