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CD-ROM: Clarify behavior when shell is opened 

Some games rely on the interrupt here, and don't send a stop command before changing discs.
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Connor McLaughlin 2021-01-28 14:37:29 +10:00 committed by GitHub
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@ -757,6 +757,14 @@ as second response byte, with the following values:<br/>
when the disk is missing, or when the drive unit is disconnected from the
mainboard.<br/>
When the shell is opened, INT5 is triggered regardless of whether a command was
executing or not. When this happens, all bits except shell open and error are cleared
in the status register. The error byte in the INT5 is set to 08h.<br/>
Some games send a Stop command before changing discs, but others just wait for the
user to open the shell, causing the disc to stop. The game can then send GetStat commands,
looping until bit 4 is cleared to detect when the new disc has been inserted.<br/>
#### Stat Seek/Play/Read bits
There's is only max ONE of the three Seek/Play/Read bits set at a time, ie.
during Seek, ONLY the seek bit is set (and Read or Play doesn't get until seek