PC87311A datasheet(36/78 Pages) NSC

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40 FDC Command Set Description (Continued)

4210 Read Deleted Data Command

The Read Deleted Data command reads logical sectors

containing a Deleted Data AM from the selected drive and

makes the data available to the host mP This command is

identical to the Read Data command except for the setting

of the CM bit in ST2 and the skipping of sectors The effect

of SK on the Read Deleted Data command is summarized in

Table 4-8 See Table 4-7 for the state of the result bytes for

a Normal Termination of the command

4211 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

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

2 Two index pulses were detected since the search began

and no AM has been found If the Address Field AM was

never found the MA bit is set in ST1

4212 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

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

2 A comparison of the sector Address Field ID bytes will be

performed except for the sector number The internal

sector address is set to 1 and then incremented for each

successive sector read

3 If the Address Field ID comparison fails the controller

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

4 Multi-track and Skip operations are not allowed SK and

MT should be set to 0

5 If there is a CRC error in the Data Field the controller

sets CE in ST1 and CD in ST2 but continues reading

sectors

6 The controller reads a maximum of EOT physical sectors

There is no support for multi-track reads

4213 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-

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

TABLE 4-9 Maximum Recalibrate Step Pulses

Based on R255 and ETR

R255

ETR

Maximum Recalibrate

Step Pulses

85 (default)

255

3925

4095

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

4214 Relative Seek Command

The Relative Seek command steps the selected drive in or

out a given number of steps This command will step the

readwrite head an incremental number of tracks as op-

TABLE 4-8 SK Effect on Read Deleted Data Command

Data Type

Sector Read

CM Bit (ST2)

Description of Results

Normal

No Further Sectors Read

Deleted

Normal Termination

Normal

Sector Skipped

Deleted

Normal Termination

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