PC87306 datasheet(41/110 Pages) NSC

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40 FDC Command Set Description (Continued)

TABLE 4-8 Sector Size Selection

Bytes per

Number of Bytes

Sector Code

in Data Field

128

256

512

1024

2048

4096

8192

16384

The controller then starts the Data Separator and waits for

the Data Separator to find the next sector Address Field

The controller compares the Address Field ID information

(track head sector bytes per sector) with the desired ID

specified in the Command Phase If the sector ID bytes do

not match then the controller waits for the Data Separator

to find the next sector Address Field The ID comparison

process repeats until the Data Separator finds a sector Ad-

dress Field ID that matches that in the command bytes or

until an error occurs Possible errors are

1 The mP aborted the command by writing to the FIFO If

there is no disk in the drive the controller hangs up The

P must then take the controller out of this hung state by

writing a byte to the FIFO This puts the controller into the

Result Phase

2 Two index pulses were detected since the search began

and no valid ID has been found If the track address ID

differs the WT bit or BT bit (if the track address is FFh) is

set in ST2 If the head sector or bytes per sector code

did not match the ND bit is set in ST1 If the Address

Field AM was never found the MA bit is set in ST1

3 The Address Field was found with a CRC error The CE

bit is set in ST1

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 within 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 Skip Flag (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 4-9

Having found the Data Field the controller then transfers

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

Section 53 Controller Phases) until the bytes per sector

count has been reached or the host terminates the opera-

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

The controller then generates the CRC for the sector and

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

Field

Having finished reading the sector the controller continues

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 is

transferred

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

set The IC bits in ST0 are set to Abnormal Termination

If Multi-Track Selector (MT) was set in the Opcode com-

mand byte and the last sector of side 0 has been trans-

ferred the controller then continues with side 1

Upon terminating the Execution Phase of the Read Data

command the controller asserts IRQ6 indicating the begin-

ning of the Result Phase The mP must then read the result

bytes from the FIFO The values that are read back in the

result bytes are shown in Table 4-10 If an error occurs the

result bytes indicate the sector read when the error oc-

curred

Command Phase

MFM

IPS

DR1

DR0

Track Number

Drive Head Number

Sector Number

Bytes per Sector

End of Track Sector Number

Intersector Gap Length

Data Length

Execution Phase

Data read from disk drive is transferred

to system via DMA or Non-DMA modes

Result Phase

Status Register 0

Status Register 1

Status Register 2

Track Number

Head Number

Sector Number

Bytes per Sector

PC87306 Datasheet(PDF) 41 Page - National Semiconductor (TI)

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