PC87309VLJ datasheet(68/192 Pages) NSC

68 / 192 page

The Floppy Disk Controller (FDC) (Logical Device 0)

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3.7.13

The READ A TRACK Command

The READ A TRACK command reads sectors from the se-

lected drive, in physical order, and makes the data available

to the host.

Command Phase

The command phase bytes of the READ A TRACK com-

mand are like those of the READ DATA command, except

for the MT and SK bits. Multi-track and skip operations are

not allowed in the READ A TRACK command. Therefore,

bits 7 and 5 of the opcode command phase byte (MT and

SK, respectively) must be 0.

First Command Phase Byte, Opcode

See “Bit 6 - Modified Frequency Modulation (MFM)” on

page 57.

Second Command Phase Byte

See “Second Command Phase Byte” on page 57 for a

description of the Drive Select (DS1,0) and Head Select

(HD) bits.

See “Bit 5 - Implied Seek (IPS)” on page 60 for a de-

scription of the Implied Seek (IPS) bit.

Third through Ninth Command Phase Bytes

See Section 3.7.10 on page 64.

Execution Phase

Data read from the disk drive is transferred to the system in

DMA or non-DMA modes. See Section 3.4.2 on page 45.

Execution of this command is like execution of the READ

DATA command except for the following differences:

The controller waits for a pulse from the INDEX signal

before it searches for the address field of a sector.

If the microprocessor writes to the FIFO before the IN-

DEX pulse is detected, the command enters the result

phase with the Interrupt Code (IC) bits (bits 7,6) in ST0

set to abnormal termination (01).

All the ID bytes of the sector address are compared, ex-

cept the sector number. Instead, the sector number is

set to 1, and then incremented for each successive sec-

tor read.

If no match occurs when the ID bytes of the sector ad-

dress are compared, the controller sets the Missing

Data bit (bit 2) in ST1, but continues to read the sector.

If there is a CRC error in the address field being read,

the controller sets CRC Error (bit 5) in ST1, but contin-

ues to read the sector.

If there is a CRC error in the data field, the controller

sets the CRC Error bit (bit 5) in ST1 and CRC Error in

Data Field bit (bit 5) in ST2, but continues reading sec-

tors.

The controller reads a maximum of End of Track (EOT)

physical sectors. There is no support for multi-track

reads.

Result Phase

3.7.14

The RECALIBRATE Command

The RECALIBRATE command issues pulses that make the

head of the selected drive step out until it reaches track 0.

Command Phase

Second Command Phase Byte

See “Second Command Phase Byte” on page 57 for a

description of the Drive Select (DS1,0) and Head Select

(HD) bits.

Execution Phase

After the last command byte is issued, the Drive Busy bit for

the selected drive is set in the Main Status Register (MSR).

See bits 3-0 in Section 3.3.5 on page 42.

The controller waits the Delay Before Processing time (see

TABLE 3-24 on page 74) for the selected drive., and then

becomes idle. See Section 3.4.4 on page 47.

Then, the controller issues pulses until the TRK0 disk inter-

face input signal becomes active or until the maximum num-

ber of RECALIBRATE step pulses have been issued.

TABLE 3-19 on page 69 shows the maximum number of

RECALlBRATE step pulses that may be issued, depending

on the RECALIBRATE Step Pulses (R255) bit, bit 0 in the

second command phase byte of the MODE command

(page 60), and the Extended Track Range (ETR) bit, bit 4 of

the third command byte of the MODE command (see Sec-

tion 3.7.7 on page 60).

If the number of tracks on the disk drive exceeds the maxi-

mum number of RECALIBRATE step pulses, it may be nec-

essary to issue another RECALIBRATE command.

76543210

MFM

000010

IPS

XXXX

DS1

DS0

Track Number

Head Number

Sector Number

Bytes-Per-Sector Code

End of Track (EOT) Sector Number

Bytes Between Sectors - Gap 3

Data Length (Obsolete)

76543210

Result Phase Status Register 0 (ST0)

Result Phase Status Register 1 (ST1)

Result Phase Status Register 2 (ST2)

Track Number

Head Number

Sector Number

Bytes-Per-Sector Code

76543210

00000111

XXXXX

DS1

DS0

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