[Coco] CoCo Disk Basic and head banging

[Robert Gault]

For most of us there will be head banging with floppies because Disk Basic ignored this issue. I wrote a patch for the Disk ROM and included code to prevent head banging regardless of the type of floppy drive. 
I assigned a byte in low RAM as last drive used. When initializing Disk Basic, that bytes was set to $FF. Each time Basic needed to read or write to a disk, the new code checked to see if the drive had changed by comparing the needed drive with LASTDR. If there was a difference, and there always was at turn on, the drive was told to read the head address: #$C0 sent to $FF48. 
So knowing where the drive head was located, there was no reason to attempt to move the head an arbitrary number of tracks to a lower number which might actually be a "negative" one.

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