| &C033 | BIOS SET MESSAGE |
| Action | Enables or disables disc error messages |
| Entry | To enable messages, A holds &00; to disable messages, A holds &FF |
| Exit | A holds the previous state, HL and the flags are corrupt, and all others are preserved |
| Notes | Enabling and disabling the messages can also be achieved by poking &BE78 with &00 or &FF |
| &C036 | BIOS SETUP DISC |
| Action | Sets the parameters which effect the disc speed |
| Entry | HL holds the address of the nine bytes which make up the parameter block |
| Exit | AF, BC, DE and HL are corrupt, and all other registers are preserved |
| Notes | The parameter block is arranged as follows bytes 0&1 - the motor on time in 20ms units; the default is &0032; the fastest is &0023 bytes 2&3 - the motor off time in 20ms units; the default is &00FA; the fastest is &00C8 byte 4 - the write off time in l0ęs units; the default is ⁡ should not be changed byte 5 - the head settle time in 1ms units; the default is &0F; should not be changed byte 6 - the step rate time in 1ms units; the default is &0C; the fastest is &0A byte 7 - the head unload delay; the default is &01; should not be changed byte 8 - a byte of &03 and this should be left unaltered |
| &C039 | BIOS SELECT FORMAT |
| Action | Sets a format for a disc |
| Entry | A holds the type of format that is to be selected |
| Exit | AF, BC, DE and HL are corrupt, and all the other registers are preserved |
| Notes | To select one of the normal disc formats, the following values should be put into the A register Data format - &C1 System format - &41 - Used by CP/M IBM format - &01 - compatible with CP/M-86 This routine sets the extended disc parameter block (XDPB) at &A890 to &A8A8 - to set other formats, the XDPB must be altered directly |
| &C03C | BIOS READ SECTOR |
| Action | Reads a sector from a disc into memory |
| Entry | HL holds the address in memory where the sector will be read to, E holds the drive number (&00 for drive A, and &01 for drive B), D holds the track number, and C holds the sector number |
| Exit | If the sector was read properly, then Carry is true, A holds 0, and HL is preserved; if the read failed, then Carry is false, A holds an error number, and HL is corrupt; in either case, the other flags are corrupt, and all other registers are preserved |
| &C03F | BIOS WRITE SECTOR |
| Action | Writes a sector from memory onto disc |
| Entry | HL holds the address of memory which will be written to the disc, E holds the drive number (&00 for drive A, and &01 for drive B), D holds the track number, and C holds the sector number |
| Exit | If the sector was written properly, then Carry is true, A holds 0, and HL is preserved; if the write failed, then Carry is false, A holds an error number, and HL is corrupt; in either case, the other flags are corrupt, and all other registers are preserved |
| &C042 | BIOS FORMAT TRACK |
| Action | Formats a complete track, inserts sectors, and fills the track with bytes of &E5 |
| Entry | HL contains the address of the header information buffer which holds the header information blocks, E contains the drive number (&00 for drive A, and &01 for drive B), and D holds the track number |
| Exit | if the formatting process was successful, then Carry is true, A holds 0, and HL is preserved; if the formatting process failed, then Carry is false, A holds an error number, and HL is corrupt; in either case, the other flags are corrupt, and all the other registers are preserved |
| Notes | The header information block is laid out as follows byte 0 - holds the track number byte 1 - holds the head number (set to zero) byte 2 - holds the sector number byte 3 - holds log2(sector size) -7 (usually either &02=512 bytes, or &03=1024 bytes). Header information blocks must be set up contiguously for every sector on the track, and in the same sequence that they are to be laid down (eg &C1, &C6, &C2, &C7, &C3, &C8, &C4, &C9, &C5) |
| &C045 | BIOS MOVE TRACK |
| Action | Moves the disc drive head to the specified track |
| Entry | E holds the drive number (&00 for drive A, and &01 for drive B), and D holds the track number |
| Exit | If the head was moved successfully, then Carry is true, A holds 0, and HL is preserved; if the move failed, then Carry is false, A holds an error number, and HL is corrupt; in both cases, the other flags are corrupt, and all other registers are preserved |
| Notes | There is normally no need to call this routine as READ SECTOR, WRITE SECTOR and FORMAT TRACK automatically move the head to the correct position |
| &C048 | BIOS GET STATUS |
| Action | Returns the status of the specified drive |
| Entry | A holds the drive number (&00 for drive A, and &01 for drive B) |
| Exit | If Carry is true, then A holds the status byte, and HL is preserved; if Carry is false, then A is corrupt, and HL holds the address of the byte before the status byte; in either case, the other flags are preserved, and all other registers are preserved |
| Notes | The status byte indicates the drive's status as follows if bit 6 is set, then either the write protect is set or the disc is missing if bit 5 is set, then the drive is ready and the disc is fitted (whether the disc is formatted or not) if bit 4 is set, then the head is at track 0 |
| &C04B | BIOS SET RETRY COUNT |
| Action | Sets the number of times the operation is retried in the event of disc error |
| Entry | A holds the number of retries required |
| Exit | A holds the previous number of retries, HL and the flags are corrupt, and all others are preserved |
| Notes | The default setting is &10, and the minimum setting is &01; the number of retries can also be altered by poking &BE66 with the required value |
| &C56C | GET SECTOR DATA |
| Action | Gets the data of a sector on the current track |
| Entry | E holds the drive number |
| Exit | If a formatted disc is present, then Carry is true, and HL is preserved; if an unforrnatted disc is present or the disc is missing, then Carry is false, and HL holds the address of the byte before the status byte; in either case, A and the other flags are corrupt, and all other registers are preserved |
| Notes | The track number is held at &BE4F, the head number is held at &BE50, the sector number is held at &BE51, and the log2(sector size)-7 is held at &BE52; disc parameters do not need to be set to the format of the disc; this routine is best used with the disc error messages turned off |