PC87309VLJ datasheet(76/192 Pages) NSC

76 / 192 page

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

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3.7.23

The VERSION Command

The VERSION command returns the version number of the

current Floppy Disk Controller (FDC).

Command Phase

Execution Phase

None.

Result Phase

The result phase byte returns a value of 90h for an FDC that

is compatible with the 82077.

Other controllers, i.e., the DP8473 and other NEC765 com-

patible controllers, return a value of 80h (invalid command).

3.7.24

The WRITE DATA Command

The WRITE DATA command receives data from the host

and writes logical sectors containing a normal data Address

Mark (AM) to the selected drive.

This command is like the READ DATA command, except

that the data is transferred from the microprocessor to the

controller instead of the other way around.

Command Phase

See Section 3.7.10 on page 64 for a description of these

bytes.

The controller waits the Delay Before Processing time be-

fore starting execution.

If implied seeks are enabled, i.e., IPS in the second com-

mand phase byte is 1, the operations performed by SEEK

and SENSE INTERRUPT commands are performed (with-

out these commands being issued).

Execution Phase

Data is transferred from the system to the controller via

DMA or non-DMA modes and written to the disk.See Sec-

tion 3.4.2 on page 45 for a description of these data transfer

modes.

The controller starts the data separator and waits for it to

find the address field of the next sector. The controller com-

pares the address ID (track number, head number, sector

number, bytes-per-sector code) with the ID specified in the

command phase.

If there is no match, the controller waits to find the next sec-

tor address field. This process continues until the desired

sector is found. If an error condition occurs, the Interrupt

Control (IC) bits (bits 7,6) in ST0 are set to abnormal termi-

nation, and the controller enters the result phase. See “Bits

7,6 - Interrupt Code (IC)” on page 48.

Possible errors are:

The microprocessor aborted the command by writing to

the FIFO.

If there is no disk in the drive, the controller gets stuck.

The microprocessor must then write a byte to the FIFO

to advance the controller to the result phase.

Two pulses of the INDEX signal were detected since the

search began, and no valid ID was found.

If the track address differs, either the Wrong Track bit

(bit 4) or the Bad Track bit (bit 1) (if the track address is

FFh is set in result phase Status register 2 (ST2). See

Section 3.5.3 on page 49.

If the head number, sector number or bytes-per-sector

code did not match, the Missing Data bit (bit 2) is set in

result phase Status register 1 (ST1).

If the Address Mark (AM) is not found, the Missing Ad-

dress Mark bit (bit 0) is set in ST1.

Section 3.5.2 on page 49 describes the bits of ST1.

A CRC error was detected in the address field. In this

case the CRC Error bit (bit 5) is set in ST1.

The controller detected an active the Write Protect (WP)

disk interface input signal, and set bit 1 of ST1 to 1.

If the correct address field is found, the controller waits for

all (conventional drive mode) or part (perpendicular drive

mode) of gap 2 to pass. See FIGURE 3-5 on page 59. The

controller then writes the preamble field, Address Marks

(AM) and data bytes to the data field. The microprocessor

transfers the data bytes to the controller.

After writing the sector, the controller reads the next logical

sector, unless one or more of the following termination con-

ditions occurs:

The DMA controller asserted the Terminal Count (TC)

signal to indicate that the operation terminated. The In-

terrupt Code (IC) bits (bits 7,6) in ST0 are set to normal

termination (00). See “Bits 7,6 - Interrupt Code (IC)” on

page 48.

The last sector address (of side 1, if the Multi-Track en-

able bit (MT) was set to 1) was equal to the End of Track

sector number. The End of Track bit (bit 7) in ST1 is set.

The IC bits in ST0 are set to abnormal termination (01).

This is the expected condition during non-DMA trans-

fers.

Overrun error. The Overrun bit (bit 4) in ST1 is set. The

Interrupt Code (IC) bits (bits 7,6) in ST0 are set to abnor-

mal termination (01). If the microprocessor cannot ser-

vice a transfer request in time, the last correctly written

byte is written to the disk.

If the Multi-Track (MT) bit was set in the opcode command

byte, and the last sector of side 0 has been transferred, the

controller continues with side 1.

76543210

MFM

000101

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)

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