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

Entry:
DE A pointer to the FCB containing the program's filespec.
Exit:
BC Returns a pointer to the start of the system command buffer.
HL Contains the error return code if an error was encountered.
7.6.80 @RWRIT SVC-70
This SVC will rewrite the current sector following a write operation. The @WRITE function
advances the Next Record Number (NRN) after the sector is written. @RWRIT will decrement
the NRN and write the disk buffer again.
Registers Affected: AF.
Entry:
DE A pointer to the FCB for the file sector to rewrite.
Exit:
A Contains an error return code if an error was encountered.
Z Set if the operation was successful.
7.6.81 @SEEK SVC-46
This SVC will pass a function code 6 to a disk driver. It is used to issue a controller
SEEK command. Disk controllers optionally verify only the track address, therefore it is
not necessary to pass a sector number to @SEEK. See chapter 4 for additional information.
Registers Affected: AF [Note: DOS saves BC, IY; drivers should save any other
registers they use].
Entry:
C Contains the logical drive number.
D Contains the logical cylinder requested.
7.6.82 @SEEKSC SVC-71
This SVC is used to seek a specified file record prior to attempting to read or write the
record. The record identified for the seek operation will be that determined by the Next
Record Number (NRN) identified in the File Control Block (FCB). The SEEK operation may
require that the current file buffer be written back to disk if it contains updated
information and the desired record is located in a different disk sector. If an error
occurs in this operation, the error code will be returned. The return code condition will
never reflect an error for the actual SEEK itself. @SEEKSC serves a useful purpose only
when asynchronous I/O is implemented permitting disk seeking external to CPU control. On
the TRS-80 Model 4, it is unnecessary.
Registers Affected: AF.
Entry:
DE A pointer to the File Control Block of the file.
Exit:
A Contains an error code if an error is encountered in writing.
Z Set will indicate that the SEEK operation "completed".
7.6.83 @SKIP SVC-72
This SVC will cause a skip past the next logical record. The SKIP operation may require
that the current file buffer be written back to disk if it contains updated information
and the desired record is located in a different disk sector. If any error is encountered
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