SEARCH - Find file in table of contents

Syntax:

CALL 402CH
Input:

  • Filename in FNAM (IY+1)

  • The drive must be powered on.

Exit:

If file exists,

  • type of file in TYPE+1 (IY+10).

  • The sector of the table of contents with the entry found is in the data buffer.

  • Register DE points to the byte after the name.

  • SCTR and TRCK contain the address of the sector.

Registers used:

AF, BC, DE, HL

Error handling:

  • A = 0 File does not exists

  • A = 2 File already exists

  • A = 9 An address mark was not found

  • A =10 A checksum error occurred during reading

  • A =13 File does not exists

  • A =17 BREAK key pressed

The SEARCH routine checks whether a file with the name stored in FNAM already exists in the table of contents of the addressed diskette.

The result of the search is transferred in the A register.

A = 2 means that there is a corresponding entry

The sector of the table of contents is in the data buffer and DE points to the byte after the name of the entry found (= address of the 1st sector of this file).

The SCTR and TRCK fields of the DOS vectors contain the sector address within the table of contents.

The TYPE+1 (IY+10) field contains the type of the found file. You may have to evaluate this yourself.

A = 0 or A = 13 have the same meaning.

The specified file is not in the table of contents of the diskette.

  • A=0 - the end of valid entries has been reached.

  • А=13 - the end of the table of contents has been reached.

All other values of A indicate an error or fact that BREAK key was pressed.

Example:

...
DI                  ; disable interrupts
LD (IY+11),10H      ; select Drive 1
CALL 4008H          ; and turn on
LD BC,50            ; 50 ms delay
CALL 4038H
CALL 4011H          ; load allocation map
LD HL,DNAM          ; filename text
CALL 401DH          ; copy filename to FNAN
CALL 4026H          ; find file in table of contents
OR A
JR Z,A1             ; unavailable!
CP 0DH
JR Z,A1             ; unavailable!
CP 2                ; error?
JP NZ,400EH         ; yes, to the ERROR routine
IN A,(13H)          ; check write protection
OR A
LD A,4
JP M,400EH          ; read only, to the ERROR routine
EX DE,HL            ; address of entry in HL
LD DE,-10           ; HL to the beginning of the entry
ADD HL,DE
LD (HL),1           ; release entry
CALL 4023H          ; write back sector of table of contents
...
...         release occupied sectors in the allocation map
...
A1: CALL 4017H      ; write back allocation map
CALL 400BH          ; turn off drive
EI                  ; enable interrupts again
...
DNAM: DEFM '"DIARY":'

The “DIARY” file, if present, is deleted from the directory of the diskette in drive 1. If not there, the delete routine is skipped.

Note that this example has not been fully coded out. In addition to deleting the entry in the table of contents, you must also release all occupied sectors of this file in the allocation map.

Internally called routines: READ