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Old 22nd Apr 2019, 11:49 pm   #69
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,483
Default Re: MK14 programming interface - MK2

I think Daver... (for the benefit of others here on this forum we are referring to a user on the Vintage Computer Forums who has made a virtual MK14 - still a work in progress - in VHDL) ... Daver would be very interested to hear your feedback on that, or might be even more interested if you fixed it first and then told him.

There is one potential problem that I can think of, and that is the way an offset of -128 is treated by some instructions and not others. For pointer instructions an offset of -128 means 'Use the current contents of the E (Extension) register as the offset', whereas with some others - jump instructions? -128 is just an offset like any other possible value.

I can't remember the specifics but I think in the case of some emulations there is an assumption that an offset value of -128 always means 'use the value in the E register as the offset for this instruction', in which case any code which happens to include a jump instruction with a -128 offset will fail.

I might not be remembering this correctly - Karen is going to be the expert on this one.

Last edited by SiriusHardware; 22nd Apr 2019 at 11:56 pm.
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