User`s guide

BDOS FUNCTION 21: WRITE SEQUENTIAL
Entry Parameters:
Registers C: 15H
DE: FCB Address
Returned Value:
Registers A: Error Code
H: Physical Error
The Write Sequential function writes 1 to 128 128-byte data records, beginning at
the current DMA address into the file named by the FCB addressed in register pair
DE. The BDOS Multi-Sector Count (see Function 44) determines the number of 128
byte records that are written. The default is one record. The referenced FCB must
have been previously activated by a BDOS Open or Make function call.
Function 21 places the record into the file at the position indicated by the cr byte
of the FCB, and then automatically increments the cr byte to the next record posi-
tion. If the cr field overflows, the function automatically opens, or creates the next
logical extent, and resets the cr field to 0 in preparation for the next write operation.
If Function 21 is used to write to an existing file, then the newly written records
overlay those already existing in the file. The calling program must set the cr field to
0 following an Open or Make call if the intent is to write sequentially from the
beginning of the file.
Function 21 makes an Update date and time for the file if the following conditions
are satisfied: the referenced drive has a directory label that requests date and time
stamping, and the file has not already been stamped for update by a previous Make
or Write function call.
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BDOS Function Calls CP/M 3 Programmers Guide