GM82C765B Datasheet, PDF (31/36 Pages) Hynix Semiconductor – FLOPPY DISK SUBSYSTEM CONTROLLER

GM82C765B
Write Data
A set of nine bytes is required to set the into
DC the Write Data mode, after the commawrite
data and has been issued the FDC loads the head
(if is in the unloaded state), waits the specified
head settling time (defined in the specify
command), and beings reading ID fields, when
all four bytes loaded during the command
(C,H,R,N) match the four byte of ID field from
the processor byte-by-byte via the data bus and
outputs it to the FDD. After writing data into the
current sector, the sector number stored in ‘Rr’ is
incremented by one, and the next data field is
written into. The FDC continues this multisector
Write Operation’ until the issuance of Terminal
Count signal. If a Terminal Count signal is sent
to the FDC it continues writing into the current
sector to complete the data field. If the Terminal
Count signal is received while a data field is
being written remainder of the data field is filled
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) flag of Status Register
1 to a 1 (high) and terminates the Write Data
command. (Status Register 0 also has bit 7 and 6
set to 0 and 1 respectively.)
The Write command operates in much the
same manner as the Read command. The
following items are the same., and one should
refer to the Read data command for details.
The Write command operates in much the
same manner as the Read command. The
following items are the same, and one should
refer to following items are the same, and one 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
In the Write Data mode, data transfers
between the processor and FDC via the data bus,
must occur every 27 uS in the FM mode and
every 13 us in the MFM mode. If the time
interval between data transfers is longer than this,
then the FDC sets the OR (Overrun) flag in
Status Register 1 to a 1 (high) and terminal the
Write Data Address mark.
Write Deleted Data
This command is the same as the Write Data
command except a Deleted Data Address mark is
written at the beginning of the data field instead
of the normal Data Address mark.
Read Deleted Data
This command is the same as the Read Data
command except that when the FDC detects a
Data Address mark at the beginning of a data
field (and SK = 0 (low)), it will read all the data
in the sector and set the CM flag in Status
Register 2 to a 1 (high), and then terminate the
command. If SK = 1, then the FDC skps the
sector with the Data Address mark and reads the
next sector.
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 of the sectors is
read. Immediately after sensing the index hole.
The FDC starts reading all data fields on the
track as continuous biocks of data.
If the FDC finds an error in the ID or Data
CRC check bytes, it continues to. 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 index
hole for the second time, it sets the MA (Missing
Address mark) flag in Status Register 1 to a 1
(high) and terminates the command. (Status
Register 0 has bits 7 and 6 set to 0 and 1
respectively.)
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