OSWORD &FB

OSWORD &FB (251) Floppy disk access

This OSWORD call is installed by the 80x86 DOS BIOS.

Commands are sent from the 80x86 via Tube Register 2 within the OSWORD protocol, so cannot be called through the normal OSWORD mechanism. The transaction must be done manually by the client by sending through Tube Register 2:

   &08 : Start OSWORD transaction
   &FB : OSWORD call &FB
   &00 : TxLen=0
   xxx : Send a series of commands
   &00 : RxLen=0, terminate the OSWORD call

Commands

• &00 : Finish
• &01 : Master FDC command
• &02 : BBC B/B+ command
• &03 : Claim Tube and NMI
• &04 : Release Tube and NMI
• &nn,&mm : Write byte &mm to &FE00+nn

FDC commands

The FDC commands &01 and &02 are followed by a parameter block:

• address b0-b7
• address b8-b15
• address b16-b23
• address b24-b31
• &00=Read from disk, <>&00-Write to disk
• error mask
• sector count
• FDC command

The initial drive, track, sector must be written to the FDC hardware beforehand using commands >&04 to write to &FE00+FDC_address.

See also

• OSWORD &FB source code
• OSWORDs list at mdfs.net

Tube OSWORD calls
OSWORD &FA : Data transfer across Tube OSWORD &FB : MFM floppy disk access OSWORD &FC : DOS CRTC control OSWORD &FD : DOS Text control	OSWORD &FE : DOS Hard disk access OSWORD &FE : Z80 FM floppy disk access OSWORD &FF : DOS Fast screen access OSWORD &FF : Data transfer across Tube

Jgharston 14:27, 26 May 2009 (UTC) Jgharston (talk) 10:54, 17 December 2024 (CET)