The FMS GET BYTE routine, DFMGET, is called directly by CIO via the FMS Device Vector Table, DFMSDH at $7GB. The GET BYTE routine's function is to get and return the next sequential data byte to CIO.
Address — $ABF
Entry Registers —
|A = Don't Care|
|Y = IOCB number times 16.|
|X = Don't Care.|
Exit Registers —
|A = Unknown.|
|Y = Unknown.|
|X = Unknown.|
1) Initialize via the SETUP routine.
2) If the FCB is opened for Directory read, then go to GDCHAR.
3) If the current sector is empty, attempt burst I/O (see Burst I/O section), then continue with number four.
4) Read the next sector via the RDNXTS routine. If the read sector operation did not return an end-of-file condition, then continue at step three, else exit via ERREOF (end-of-file error).
5) Get the data byte from the sector and place it in SVDBYT for the exit routines.
6) If the next byte in the file is the end-of-file byte, exit via RETURN with the impending end-of-file condition code ($03), else exit via GREAT.
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