Actually I'm wrong here...Yes, the GODIL ICE will change the value read with no 6850 from &FE to &FF.Would the ICE being fitted affect the 'read' from a non-fitted 6850?
I just checked, and with no 6850 &FE08/&FE09 return &00, and the Beeb boot normally. I wasn't expecting this, as other unused Shiela addresses (like the Tube) return &FE.
Maybe the difference is the &FEE0-&FEFF is accessed at 2MHz, where as &FE00-&FE1F is accessed at 1MHz. So there is more time for the 6K8 data bus pulldowns (RP1) to take effect (the previous bus cycle is generally the high byte of the address, &FE in this case).
But the GODIl wll definitely mess this up, and make the MOS think the ACIA is interrupting all the time.
So Roland, re-fit the ACIA and then put a watch point on DCA9 (not DCA2) to see if the ACIA really is interrupting.
Dave
Statistics: Posted by hoglet — Wed Jan 31, 2024 11:04 pm