gm82c765b ETC-unknow, gm82c765b Datasheet - Page 29

• Manufacturer Part Number: gm82c765b
• Description: Floppy Disk Subsystem Controller
• Manufacturer: ETC-unknow

COMMAND DESCRIPTIONS
Read Data
A set of nine byte words are required to place the
FDC into the Read Data Mode.
After the Read Data command has been issued,
the FDC loads the head (if it is unloaded state),
warts the specified head setting time (defined in
the Specify Command begins reading ID Address
Marks and ID fields. When the current sector
number (“R”) stored in the ID Register (IDR)
compares with the sector number read off the
diskette, then the FDC outputs data (from the
data bit) byte-to-byte to the main system via the
data bus.
After completion of the read operation from the
current sector, the Sector number is incremented
by one, and the data from the next sector is read
and output on the data bus.
This continuous read function is called a
“Multi-sector Read Operation.” The Read Data
Command may be terminated by the receipt of a
Terminal Count signal.
TC should be issued at the same time that the
N
NCN
ND
PCN
R
R/W
SC
SK
SRT
ST0
ST1
ST2
ST3
STP
US0, US1
SYMBOL
NUMBER
NEWCYLINDER
NUMBER
NON-DMA MODE
PRESENT CYLINDER
RECORD
READ/WRITE
SECTOR
SKIP
STEP RATE TIME
STATUS 0
STATUS 1
STATUS 2
STATUS 3
UNIT SELECT
NAME
DESCRIPTION
N stands for the NUMBER of data bytes written in a sector.
NCN stands for a NEW CYLINDER NUMBER which is going to be reached as
a result of the Seek operation. Desired position of head.
ND stands for operation in the NON-DMA MODE.
PCN stands for the cylinder number at the completion of the SENSE
INTERRUPT STATUS Command position of head at present time..
R stands for the sector number which will be read or written.
R/W stands for either READ or WRITE signal.
SC indicates the number of sectors per cylinder.
SK stands for SKIP Deleted Data Address mark.
STR stands for the Stepping Rate for the FDD (1 to 16ms in 1ms increments).
Stepping Rate applies to all drives. In 2’s complement format, F(Hes) = 1ms,
E(Hex) =2ms, etc
STO = 3 stands for one of four registers which store the STATUS information
after a command has been executed. This information is available during the
result phase after command execution.
These registers should not be confused with the main Status Register (selected by
A0 = 0). ST0=3 may be read only after 3 command has been executed and
contains information relevant to that particular command.
During a SCAN operation, if STP=1, the data in contiguous sectors is compared
byte by byte with data sent from the processor (or DMA); if STP=2, then
alternate sectors are read and compared.
US stands for a selected drive; binary encoded, 1 of 4.
29
Upon receipt of this signal, the FDC stops
outputting data to the processor, but will continue
to read data from the current sectors, check CRC
(Cyclic Redundancy Count) bytes, and the end of
the sector terminate the read data command.
The amount of data which can be handled with a
single command to the FEC depends upon MT
(multi-track), MF(MFM/FM), and N(number of
bytes/sector). Table 27 lists the transfer Capacity.
The “Multi-track” function (MT) allows the FDC
to read data from both sides of the diskette. For a
particular cylinder, data will be transferred
starting at Sector 1, Side 0 and
completing at Sector L, Side 1 (Sector L = last
sector on the side). Note, this function pertains to
only one cylinder (the same track) on each side of
the diskette.
which the FDC must treat as a sector. If DTL is
smaller than the actual data length in a sector, the
DACK
When N=0, then DTL defines the data length
for the last byte of data is sent.
GM82C765B