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System register map

Address Label Description
FD00 Place of the file in the library
Bit # Description
07-04 Library sector (0-15)
03-00 Library offset (0-240 step 16)
FD01 Select code of the disk
Bit # Description
07 Delete protected file
06 Write protected file
05 Place is reserved for file
02-00Drive number
FD02-FD03 Actual logic record number
FD04-FD05 Logic record number in actial bitmapgroup
FD06-FD07 Actual bitmapgroup
FD08-DF09 Physical startrecord of the file
FD0A-FD0B Highest logic record number in the file
FD0C-FD0D Actual random access record in buffer
FD0E-FD11 Position in buffer
FD12-FD13 Pointer: DOSBUF0 start address
FD14 Number of current DOSBUF multiplied by 10h
FD15 Disk error code
Bit # Description
07 Not ready
06 Write protected
04 Not found (disk error)
03 CRC error
01 Command error (Invalid command for disk controller)
00 Busy
FD16-FD17 (unused)
FD18 Retry-count (start value is 5 or 3)
FD19-FD1B (unused)
FD1D-FD1E BC SAVE Available space for BC-register
FD1F-FD20 DE SAVE Available space for DE-register
FD21-FD22 ON ERR 35 Vector: ERROR 35 (address from FD33h if zero)
FD23-FD24 ON ERR 36 Vector: ERROR 36 (address from FD33h if zero)
FD25-FD26 ON ERR 37 Vector: ERROR 37 (address from FD33h if zero)
FD27-FD28 ON ERR 38 Vector: ERROR 38 (address from FD33h if zero)
FD29-FD2A ON ERR 39 Vector: ERROR 39 (address from FD33h if zero)
FD2B-FD2C ON ERR 40 Vector: ERROR 40 (address from FD33h if zero)
FD2D-FD2E ON ERR 41 Vector: ERROR 41 (address from FD33h if zero)
FD2F-FD30 ON ERR 42 Vector: ERROR 42 (address from FD33h if zero)
FD31-FD32 ON ERR 43 Vector: ERROR 43 (address from FD33h if zero)
FD33-FD34 ON ERR DEF Vector: Default error
FD35-FD3F (unused)
FD40 DOS logic file tables, containing as follows
Offset Size Description
00 Byte Unit number (0-31) or FFh if not specified
01 Byte FFh
02 8-byte File name
0A 3-byte File type or spaces
0D 3-byte Drive name or spaces

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This page has been created by Sami Rautiainen.
Read the small print. Last updated September 05, 2020.