Hello, * On Fri, Feb 23, 2024 at 02:30:59PM +0100 Francesco Messineo wrote: > FF57 A5 7B LDA ADRSED ; drive primary addressed? > FF59 D0 0B BNE LFF66 ; yes, move head [...] > Does anyone know why the track0 sensing code needs to check if the > drive is "primary addressed"? I suspect this page zero location was > used for other purposes on both the 1541C and the 1571 but I can't > make sense of the few places where the code writes to it. I had a quick glance at the code. My first estimation is this: This address ADRSED ($7B) is written to only in the functions FFA1 and FFA6 (1570/1571 ROM). FFA1 is called from D610. It is the function which tries to set the head to the next or previous half-track in order to resolve a read problem. This test allows for the positioning on a half-track "-0.5", so to speak. FFA6 is called from D628. It moves the head back to the full-track. So, this code is making a special case to be able to move the head one step beyond track 0. Regards, Spiro -- Spiro R. Trikaliotis https://spiro.trikaliotis.net/Received on 2024-02-23 16:00:05
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