GM82C803CN Datasheet, PDF (49/84 Pages) List of Unclassifed Manufacturers – 2.88 MB FDC/ Dual UARTs with FIFO/PIO(EPP/ ECP)/ IDE Interface/ S-IR/ PnP

GM82C803CN
Write Data
A set of nine bytes is required to set the FDC into the Write Data mode. After the Write Data command has been issued
the FDC loads the head (if it is the unloaded state), waits the specified head settling time (defined in the Specify comm-
and), and begins reading ID fields. When all four bytes loaded during the command (C,H,R,N) match the four bytes of
the ID field from the diskette, the FDC takes data from the processor byte by byte via FIFO and outputs it to the FDD.
After writing data into the current sector, the sector number stored in R is incremented by one, and the next data field
is written into. The FDC continues this multisector Write operation until the issuance of a TC signal. If a TC is sent to
the FDC it continues writing into the current sector to complete the data field. If the TC is received while a data field
is being written, then the remainder of the data field is filled with zeros. The FDC reads the ID field of each sector and
checks the CRC bytes. If the FDC detects a read error (CRC error) in one of the ID fields, it sets the DE(data error) fl-
ag of Status Register 1 to a 1 and terminates the Write Data command. (Status Register 0 also has bits 7 and 6 set to 0
and 1 respectively.)
The Write data command operates in much the same manner as the Read Data command. The following items are the
same, and one should refer to the Read Data command for details;
- Transfer capacity
- EN(End of Cylinder) flag
- ND(No Data)flag
- Head Unload Time interval
- ID information when the processor terminates command
- Definition of DTL when N=0 and when N 0
Write Deleted Data
This command is the same as the Write Data command except a Deleted Data Address Mark is written at the begin-
ning of the data field instead of the normal Data Address Mark.
Read a Track
This command is similar to the Read Data command except that this is a continuous read operation where the entire data
field from each of the sectors is read. Immediately after sensing the index hole, the FDC starts reading all data fields on
the track as continuous blocks of data. If the FDC finds an error in the ID or data CRC check bytes, it continues to read
data from the track. The FDC compares the ID information read from each sector with the value stored in the IDR and
sets the ND flag of Status Register 1 to a 1 if there is no comparison . Multitrack or skip operations are not allowed with
this command. This command terminates when the number of sectors read is equal to EOT. If the FDC does not find an
ID Address Mark on the diskette after it senses the index hole for the second time, it sets the MA(Missing Address mark)
flag in Status Register 1 to 1 and terminates the command. (Status Register 0 has bits 7 and 6 set to 0 and 1 respectively.)
Read ID
The Read ID command is used to give the present position of the recording head. The FDC stores the values from the
first ID field it is able to read if no proper ID Address Mark is found on the diskette before the index hole is encountered
for second time, then the MA flag in Status Register 1 is set to a 1 and if no data is found then the ND(No Data) flag is
also set in Status Register 1 to a 1. The command is then terminated with bits 7 and bit 6 in Status Register 0 set to 0 and
1 respectively . During this command there is no data transfer between FDC and the Host except during the result phase.