
39
N
SECTOR SIZE
00
01
02
03
..
07
128 bytes
256 bytes
512 bytes
1024 bytes
...
16 Kbytes
Table 19 - Description of Command Symbols
SYMBOL
NAME
DESCRIPTION
NCN
New Cylinder
Number
The desired cylinder number.
ND
Non-DMA Mode
Flag
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 nDACK
signals.
OW
Overwrite
The bits D0-D3 of the Perpendicular Mode Command can only be
modified if OW is set to 1. OW id defined in the Lock command.
PCN
Present Cylinder
Number
The current position of the head at the completion of Sense
Interrupt Status command.
POLL
Polling Disable
When set, the internal polling routine is disabled.
When clear,
polling is enabled.
PRETRK
Precompensation
Start Track
Number
Programmable from track 00 to FFH.
R
Sector Address
The sector number to be read or written. In multi-sector transfers,
this parameter specifies the sector 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 command.
SC
Number of
Sectors Per Track
The number of sectors per track to be initialized by the Format
command. The number of sectors per track to be verified during a
Verify command when EC is set.
SK
Skip Flag
When set to 1, sectors containing a deleted data address mark will
automatically be skipped during the execution 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.