ACT apricot - Page 116

FLOPPY DISK INTERFACE
from the disk, causes the FDC to set the Lost Data bit in the
Status Register.
If a single sector read operation was specified by the Read
Sector command, the sequence terminates with the FDC
testing the CRC character at the end of the data field. If the
CRC character is incorrect, the CRC Error bit is set within
the Status Register.
If the Read sector command specified a multiple sector
transfer,
the Sector Register is incremented and the process
repeated for
the next sector, providing the CRC character
tested at the end of the previous data field was true. If the
CRC character was incorrect, the multiple sector routine is
prematurely aborted.
If no CRC Errors are detected, the multiple sector
operation
continues until terminated either by issuing a
Force
Interrupt command, or after the sector number is
incremented to a value exceeding the number of sectors on
the track. In the latter case, the FDC automatically
terminates the command after five revolutions of the disk,
since
the verification of the ID field will not be able to
locate a
matching sector number.
Status Register. The format of the Status Register following
a data transfer
command is as detailed below. On issuing a
command to the Command Register, the FDC resets the
Status Register to monitor certain status conditions implied
by the new command. Due to internal timing delays, the
Status Register does not contain valid status information,
until 14 JLS after the new command is issued.