GM82C803CN Datasheet, PDF (46/84 Pages) List of Unclassifed Manufacturers – 2.88 MB FDC/ Dual UARTs with FIFO/PIO(EPP/ ECP)/ IDE Interface/ S-IR/ PnP

GM82C803CN
NCN New Cylinder Number. It is going to be reached as a result of the seek operation.
Desired position of head.
ND
Non-DMA mode. When set to 1, indicates that the FDC is to operate in the non-DMA mode. In this mode, the
Host is interrupted for each data transfer. When set to 0, the FDC operates in DMA mode. interfacing to a DMA
controller by means of the DRQ and DACK signals.
OW
The bits denoted D0, D1, D2, and D3 of the perpendicular Mode command can only be overwritten when this
bit is set to 1.
PCN Present Cylinder Number. The current position of the head at the completion of sense Interrupt Status comman-
d.
POLL Polling Disable. When set to 1, the internal polling routine is disabled. When 0, polling is enabled.
PRETRK Precompensation start track number. Programmable from track 00H to FFH.
R
Sector address. The sector number toe read or written. In multi-sector transfers, this parameter specifies the se-
ctor number of the first sector to be read or written.
RCN Relative Cylinder Number. Relative cylinder offset from present cylinder as used by the Relative Seek comma -
nd.
SC
Number of Sectors. The number of sectors to be initialized by the format command. The number of sectors to b-
e verified during a Verify command, When EC is set to 1.
SK
Skip. When set to 1, sectors containing a deleted data address mark will automatically be skipped during the ex-
ecution of Read Data. If Read Deleted is executed, only sectors with a deleted address mark will be accessed.
When set to 0, the sector is read or written the same as the Read and Write commands.
SRT Step Rate Time. The time interval between step pulse issued by the FDC.
Programmable from 0.5 to 8ms, increments of 0.5ms at the 1 Mbps data rate. See Specify command.
ST0-3 Status register 0-3. It stands for one of the four registers which store the status information after a command has
been executed. This information is available during the result phase after command execution. ST0-3 may be r-
ead only after a command has been executed and contains information relevant to that particular commands.
STP
During a scan operation, if STP is set to 1, the data in contiguous sectors is compared byte by byte with data s-
ent from the Host; if STP is set to 2, then alternate sectors are read and compared.
COMMAND DESCRIPTION
During the command phase, the main status register must be polled by the host before each byte is written into the data re-
gister. The DIO(bit6) and RQM(bit7) bits in the main status register must be in the 0 and 1 states respectively. before each
byte of the command may be written into the FDC. The beginning of the execution phase for any of these commands will
cause DIO and RQM to switch to 1 and 0 states respectively.
Read Data
A set of nine byte words are required to placed the FDC into the Read Data mode. After the Read Data command has been
issued, the FDC loads the head, if it is in the unloaded state, waits the specified head settling time defined in the specify c-
ommand and begins regarding ID address mark and ID fields. When the current sector number stored in the ID register co-
mpares with the sector number read off the diskette, then the FDC outputs data from the data field byte by byte to the main
system via FIFO.
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 function is called a multi sector read operation. The Re-
ad Data command must be terminated by the receipt of a Terminal Count signal. TC should be issued at the same time tha-
t the DACK for the last byte of data is sent. Upon receipt of this signal, the FDC stops outputting data to the processor. but
will continue to read data from the current sector. check CRC Cycle Redundancy Count1 bytes, and then at the end of the
sector terminate the Read Data command. The amount of data which can be handled with a single command to the FDC d-
epends upon MT(multitrack), MF(MFM/FM), and N(number of bytes/sector). Table 4-20 lists the transfer capacity.