PC8477B datasheet(27/54 Pages) NSC

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40 Command Set Description (Continued)

4215 Scan Commands

The Scan commands allow data read from the disk to be

compared against data sent from the mP There are three

Scan commands to choose from

Scan Equal

Disk Data e mP Data

Scan Low or Equal

Disk Data s mP Data

Scan High or Equal

Disk Data t mP Data

Each sector is interpreted with the most significant bytes

first If the Wildcard mode is enabled in the Mode command

an FF (hex) from either the disk or the mP is used as a don’t

care byte that will always match equal After each sector is

read if the desired condition has not been met the next

sector is read The next sector is defined as the current

sector number plus the Sector Step Size specified The

Scan command will continue until the scan condition has

been met or the EOT has been reached or if TC is assert-

Read errors on the disk will have the same error conditions

as the Read Data command If the SK bit is set sectors with

deleted data marks are ignored If all sectors read are

skipped the command will terminate with D3 of ST2 set

(Scan Equal Hit) The Result Phase of the command is

shown in Table 4-10

TABLE 4-10 Scan Command Termination Values

Command

Status

Conditions

Scan Equal

Disk e mP

Disk i mP

Scan Low

Disk e mP

or Equal

Disk k mP

Disk l mP

Scan High

Disk e mP

or Equal

Disk k mP

Disk l mP

4216 Seek Command

The Seek command issues step pulses to move the select-

ed drive head in or out until the desired track number is

reached During the Execution Phase of the Seek com-

mand the track number to seek to is compared with the

present track number The controller will determine how

many step pulses to issue and the DIR disk interface output

will indicate which direction the RW head should move

The DRx BUSY bit is set in the MSR for the appropriate

drive The controller will wait the Motor On time before issu-

ing the first step pulse

After the Motor On time the controller will enter the Idle

Phase The execution of the actual step pulses occurs in the

Drive Polling phase of the controller The step pulse rate is

determined by the value programmed in the Specify com-

mand An interrupt will be generated one step pulse period

after the last step pulse is issued There is no Result Phase

A Sense Interrupt command should be issued to determine

the cause of the interrupt

While the internal microengine is capable of multiple seeks

on 2 or more drives at the same time software should en-

sure that only one drive is seeking or recalibrating at a time

This is because the drives are actually selected via the

DOR which can only select one drive at a time No other

command except a Sense Interrupt command should be is-

sued while a Seek command is in progress

If the extended track range mode is enabled with the ETR

bit in the Mode command a fourth command byte should be

written in the Command Phase to indicate the four most

significant bits of the desired track number Otherwise only

three command bytes should be written

4217 Sense Drive Status Command

The Sense Drive Status command returns the status of the

selected disk drive in ST3 This command does not gener-

ate an interrupt

4218 Sense Interrupt Command

The Sense Interrupt command is used to determine the

cause of interrupt when the interrupt is a result of the

change in status of any disk drive Four possible causes of

the interrupt are

1 Upon entering the Result Phase of

a Read Data command

b Read Deleted Data command

c Read a Track command

d Read ID command

e Write Data command

f Write Deleted Data command

g Format command

h Scan command

i Verify command

2 During data transfers in the Execution Phase while in the

Non-DMA mode

3 Ready Changed State during the polling mode for an in-

ternally selected drive (Occurs only after a hardware or

software reset)

4 Seek Relative Seek or Recalibrate termination

An interrupt due to reasons 1 and 2 does not require the

Sense Interrupt command and is cleared automatically This

interrupt occurs during normal command operations and is

easily discernible by the mP via the MSR This interrupt is

cleared reading or writing information fromto the Data Reg-

ister (FIFO)

Interrupts caused by reason 3 and 4 are identified with the

aid of the Sense Interrupt command The interrupt is cleared

after the first result byte has been read Use bits 5 6 and 7

of ST0 to identify the cause of the interrupt as shown in

Table 4-11

TABLE 4-11 Status Register 0 Termination Codes

Status Register 0

Cause

Interrupt

Seek

Code

End

Internal Ready Went True

Normal Seek Termination

Abnormal Seek Termination

Issuing a Sense Interrupt command without an interrupt

pending is treated as an Invalid command If the extended

track range mode is enabled a third byte should be read in

the Result Phase which will indicate the four most signifi-

cant bits of the present track number Otherwise only two

result bytes should be read

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