PC8477B datasheet(25/54 Pages) NSC

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40 Command Set Description (Continued)

Once the desired sector Address Field is found the control-

ler waits for the Data Separator to find the subsequent Data

Field for that sector If the Data Field (normal or deleted) is

not found with the expected time the controller terminates

the operation and enters the Result Phase (MD is set in

ST2) If a Deleted Data Mark is found and SK was set in the

Opcode command byte the controller skips this sector and

searches for the next sector Address Field as described

above The effect of SK on the Read Data command is

summarized in Table 4-6

Having found the Data Field the controller then transfers

data bytes from the disk drive to the host (described in Sec-

tion 53 Controller Phases) until the bytes per sector count

has been reached or the host terminates the operation

(through TC end of track or implicitly through overrun) The

controller will then generate the CRC for the sector and

compare this value with the CRC at the end of the Data

Field

Having finished reading the sector the controller will contin-

ue reading the next logical sector unless one or more of the

following termination conditions occurred

1 The DMA controller asserted TC The IC bits in ST0 are

set to Normal Termination

2 The last sector address (of side 1 if MT was set) was

equal to EOT The EOT bit in ST1 is set The IC bits in

ST0 are set to Abnormal Termination This is the expect-

ed condition during Non-DMA transfers

3 Overrun error The OR bit in ST1 is set The IC bits in ST0

are set to Abnormal Termination If the mP cannot service

a transfer request in time the last correctly read byte will

be transferred

4 CRC error The CE bit in ST1 and CD bit in ST2 are set

The IC bits in ST0 are set to Abnormal Termination

If MT was set in the Opcode command byte and the last

sector of side 0 has been transferred the controller will then

continue with side 1 starting with sector 1 and continuing

until EOT sector number is reached or TC occurs

Upon terminating the Execution Phase of the Read Data

command the controller will assert INT indicating the be-

ginning of the Result Phase The mP must then read the

result bytes from the FIFO The values that will be read back

in the result bytes are shown in Table 4-7 If an error occurs

the result bytes will indicate the sector read when the error

occurred

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

TABLE 4-6 SK Effect on Read Data Command

Data Type

Sector Read

CM Bit (ST2)

Description of Results

Normal

Normal Termination

Deleted

No Further Sectors Read

Normal

Normal Termination

Deleted

Sector Skipped

TABLE 4-7 Result Phase Termination Values with No Error

Last Sector

ID Information at Result Phase

Track

Head

Sector

BytesSector

EOT

S a 1NC

EOT

T a 1NC

EOT

S a 1NC

EOT

T a 1NC

EOT

S a 1NC

EOT

T a 10

EOT

S a 1NC

EOT

T a 10

EOT e End of Track Sector Number from Command Phase

NC e No Change in Value

S e Sector Number last operated on by controller

T e Track Number programmed in Command Phase

H e Head last selected by controller

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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