The Programmer's Guide to TRSDOS Version 6 - Tim Mann's Home ...

7.6.18 @DCSTAT SVC-40
This SVC passes a function 0 to a disk driver. It is commonly used for testing the status
of a logical drive. A disk driver should return with no error on function 0. Thus, if a
particular drive is disabled, the system will return an error-32 to the calling program.
Chapter 4 has more information.
Registers Affected: AF [Note: DOS saves BC, IY; drivers should save any other
registers they use].
Entry:
C Logical drive number (0-7).
Exit:
A Error return code, if any.
Z Set if the operation was successful.
7.6.19 @DEBUG SVC-27
This SVC will force the system to enter the DEBUGging package.
Registers Affected: None except those changed by the user.
7.6.20 @DECHEX SVC-96
This SVC performs the conversion of a decimal string of digits to their binary
value in a 16-bit field. Overflow is not trapped. The conversion stops on the first digit
found not to be in the range . The linkage is:
Registers Affected: AF, BC, HL.
Entry:
HL => A pointer to your decimal string.
Exit:
BC Returns the resultant 16-bit binary value of "string".
HL Points to 1st non-decimal digit.
Z-flag is indeterminate
7.6.21 @DIRRD SVC-87
This SVC will read a directory sector containing the directory entry for a specified
Directory Entry Code (DEC). The sector will be written to the system buffer, SBUFF$, and
the register pair HL will point to the first byte of the directory entry specified by the
DEC. Note that this is a method to recover the page address of the system's buffer by
keeping register-H after an @DIRRD invocation. See the sections on HASH INDEX TABLE and
DIRECTORY RECORD FORMAT for additional information.
Registers Affected: AF, HL.
Entry:
B Directory Entry Code of the file.
C Logical drive number (0-7).
Exit:
HL Points to the DEC's directory entry.
A Error return code, if any.
Z Set if no error is encountered.
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