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Unofficial Name: FindOSHeaderSubField

BCALL Address: 8075

Search for a subfield of the given app or OS header.


  • AHL = address of the first type byte of the field whose contents you want to search (8000h if you want to search an installed app/OS header)
  • DE = field to search for (e.g. 8010 to search for the key ID)


  • HL = address of the first type byte of the first matching field
  • NZ set if not found.



This routine requires that the byte it start at not be set to FF (i.e., empty space) or 00 (i.e., a deleted application.) The OS uses this routine to search for data in its own header.

It is approximately the same as FindSubField, but handles an initial long-size field correctly, doesn't handle an initial nibble-size field correctly, and stops at any major type other than those allowed for apps (80h, 2, and 3.)

It is much like the other field search routines, but starts by skipping to the data section of the given field, and continues from there.

It does not keep track of whether the "subfield" is actually within the parent field; it simply stops when it reaches a non-app field.

See also FindAppHeaderSubField.