pc8477b National Semiconductor Corporation, pc8477b Datasheet - Page 26

• Manufacturer Part Number: pc8477b
• Description: Advanced Floppy Disk Controller
• Manufacturer: National Semiconductor Corporation

4 0 Command Set Description
4 2 11 Read ID Command
The Read ID command finds the next available Address
Field and returns the ID bytes (track head sector bytes per
sector) to the mP in the Result Phase There is no data
transfer during the Execution Phase of this command An
interrupt will be generated when the Execution Phase is
completed
The controller first simulates the Motor On time for the se-
lected drive internally The user must turn on the drive motor
directly by enabling the appropriate drive and motor select
disk interface outputs with the Digital Output Register
(DOR) The Read ID command does not perform an implied
seek
After waiting the Motor On time the controller starts the
Data Separator and waits for the Data Separator to find the
next sector Address Field If an error condition occurs the
IC bits in ST0 are set to Abnormal Termination and the
controller enters the Result Phase Possible errors are
1 The mP aborted the command by writing to the FIFO If
2 Two index pulses were detected since the search began
4 2 12 Read A Track Command
The Read a Track command reads sectors in physical order
from the selected drive and makes the data available to the
host This command is similar to the Read Data command
except for the following differences
1 The controller waits for the index pulse before searching
2 A comparison of the sector Address Field ID bytes will be
3 If the Address Field ID comparison fails the controller
4 Multi-track and Skip operations are not allowed SK and
5 If there is a CRC error in the Data Field the controller
6 The controller reads a maximum of EOT physical sectors
4 2 13 Recalibrate Command
The Recalibrate command is very similar to the Seek com-
mand The controller sets the Present Track Register (PTR)
of the selected drive to zero It then steps the head of the
selected drive out until the TRK0 disk interface input signal
goes active or until the maximum number of step pulses
have been issued See Table 4-9 for the maximum recali-
there is no disk in the drive the controller will hang up
The mP must then take the controller out of this hung
state by writing a byte to the FIFO This will put the con-
troller into the Result Phase
and no AM has been found If the Address Field AM was
never found the MA bit is set in ST1
for a sector Address Field If the mP writes to the FIFO
before the index pulse the command will enter the Result
Phase with the IC bits in ST0 set to Abnormal Termina-
tion
performed except for the sector number The internal
sector address is set to 1 and then incremented for each
successive sector read
sets ND in ST1 but continues to read the sector If there
is a CRC error in the Address Field the controller sets CE
in ST1 but continues to read the sector
MT should be set to 0
sets CE in ST1 and CD in ST2 but continues reading
sectors
There is no support for multi-track reads
(Continued)
26
brate step pulse values based on the R255 and ETR bits in
the Mode command If the number of tracks on the disk
drive exceeds the maximum number of recalibrate step
pulses another Recalibrate command may need to be is-
sued
After the last command byte is issued the DRx BUSY bit is
set in the MSR for the selected drive The controller will
simulate the Motor On time and then enter the Idle Phase
The execution of the actual step pulses occurs while the
controller is in the Drive Polling Phase An interrupt will be
generated after the TRK0 signal is asserted or after the
maximum number of recalibrate step pulses are issued
There is no Result Phase Recalibrates on more than one
drive at a time should not be issued for the same reason as
explained in the Seek command No other command except
the Sense Interrupt command should be issued while a Re-
calibrate command is in progress
4 2 14 Relative Seek Command
The Relative Seek command steps the selected drive in or
out a given number of steps This command will step the
read write head an incremental number of tracks as op-
posed to comparing against the internal present track regis-
ter for that drive The Relative Seek parameters are defined
as follows
DIR Read Write Head Step Direction Control
RTN Relative Track Number This value will determine how
The controller will issue RTN number of step pulses and
update the Present Track Register for the selected drive
The one exception to this is if the TRK0 disk input goes
active which indicates that the drive read write head is at
the outermost track In this case the step pulses for the
Relative Seek are terminated and the PTR value is set ac-
cording to the actual number of step pulses issued The
arithmetic is done modulo 255 The DRx BUSY bit in the
MSR is set for the selected drive The controller will simu-
late the Motor On time before issuing the step pulses After
the Motor On time the controller will enter the Idle Phase
The execution of the actual step pulses occurs in the Idle
Phase of the controller
After the step operation is complete the controller will gen-
erate an interrupt There is no Result Phase Relative Seeks
on more than one drive at a time should not be issued for
the same reason as explained in the Seek command No
other command except the Sense Interrupt command
should be issued while a Relative Seek command is in prog-
ress
R255
many incremental tracks to step the head in or out
from the current track number
0
1
0
1
0
1
e
e
TABLE 4-9 Maximum Recalibrate Step
Step Head Out
Step Head In
Pulses Based on R255 and ETR
ETR
0
0
1
1
Maximum Recalibrate
Step Pulses
85 (default)
3925
4095
255