The Format command terminates when the index hole is

detected a second time at which point an interrupt is gener-

ated Only the first three status bytes in the Result Phase

are significant The Format Gap byte in the Command

Phase is dependent on the data rate and type of disk drive

and will control the length of GAP3 Some typical values for

the programmable GAP3 are given in Table 4-1 below

Fig-

ure 4-1 shows the track format for the different formats rec-

ognized by the Format Command

424 Invalid Command

If an invalid command (illegal Opcode byte in the Command

Phase) is received by the controller the controller will re-

spond with ST0 in the Result Phase The controller does not

generate an interrupt during this condition Bits 6 and 7 in

the MSR are both set to a 1 indicating to the mP that the

controller is in the Result Phase and the contents of ST0

must be read The system will read an 80 (hex) value from

ST0 indicating an invalid command was received

TABLE 4-1 Typical Format Gap Length Values

Mode

Sector

Sector

EOT

Sector

Format

Size

Code

Gap

GAP3

Decimal

Hex

Hex

Hex

Hex

125 kbs

128

00

12

07

09

FM

128

00

10

10

19

256

01

08

18

30

512

02

04

46

87

1024

03

02

C8

FF

2048

04

01

C8

FF

250 kbs

256

01

12

0A

0C

MFM

256

01

10

20

32

512

02

08

2A

50

512

02

09

2A

50

1024

03

04

80

F0

2048

04

02

C8

FF

4096

05

01

C8

FF

250 kbs

128

00

1A

07

1B

FM

256

01

0F

0E

2A

512

02

08

1B

3A

1024

03

04

47

8A

2048

04

02

C8

FF

4096

05

01

C8

FF

500 kbs

256

01

1A

0E

36

MFM

512

02

0F

1B

54

512

02

12

1B

6C

1024

03

08

35

74

2048

04

04

99

FF

4096

05

02

C8

FF

8192

06

01

C8

FF

Note

FM mode is not guaranteed through functional testing

Typical Values for PC Compatible Diskette Media

Media

Sector

Sector

EOT

Sector

Format

Type

Size

Code

Gap

GAP

Decimal

Hex

Hex

Hex

Hex

360K

512

02

09

2A

50

12M

512

02

0F

1B

54

720K

512

02

09

1B

50

144M

512

02

12

1B

6C

288M

512

02

24

1B

53

Notes

Sector Gap refers to the Intersector Gap Length parameter specified in the Command Phase of the Read Write Scan and Verify commands Although this is the

recommended value the PC8477B treats this byte as a don’t care in the Read Write Scan and Verify commands

Format Gap is the suggested value to use in the Format Gap parameter of the Format command This is the programmable GAP3 as shown in

Figure 4-1

The 288M diskette media is a new Barium Ferrite media intended for use in Perpendicular Recording drives at the data rate of up to 1 Mbs

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