Table 18 - Description of Command Symbols
DESCRIPTION
SYMBOL
NCN
NAME
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
PRETRK
Polling Disable
When set, the internal polling routine is disabled. When clear, polling
is enabled.
Precompensation Programmable from track 00 to FFH.
Start Track
Number
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
SC
Relative Cylinder
Number
Relative cylinder offset from present cylinder as used by the Relative
Seek command.
Number of Sectors The number of sectors per track to be initialized by the Format
Per Track
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.
SRT
Step Rate Interval The time interval between step pulses issued by the FDC.
Programmable from 0.5 to 8 milliseconds in increments of 0.5 ms at
the 1 Mbit data rate. Refer to the SPECIFY command for actual
delays.
ST0
Status 0
Status 1
Status 2
Status 3
Write Gate
Registers within the FDC which store status information after a
command has been executed. This status information is available to
the host during the result phase after command execution.
ST1
ST2
ST3
WGATE
Alters timing of WE to allow for pre-erase loads in perpendicular
drives.
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