PC87306 datasheet(39/110 Pages) NSC

39 / 110 page

40 FDC Command Set Description (Continued)

TABLE 4-4 DENSEL Encoding

Mode Command

Pin Definition

DENSEL

Bit 1

Bit 0

Pin Low

Pin High

Undefined

DEFAULT

BFR

CMOS Disk Interface Buffer Enable

0 e Drive output signals configured as standard 4 mA

push-pull outputs (actually 40 mA sink 4 mA

source)

1 e

Drive output signals configured as 40 mA open-

drain outputs

WLD

Scan Wild Card

0 e An FFh from either the mP or the disk during a

Scan command is interpreted as a wildcard

character that always matches true

1 e

The Scan commands do not recognize FFh as a

wildcard character

Head

Settle

Time allowed for readwrite head to settle after a

seek during an Implied Seek operation This is con-

trolled as shown in Table 4-5 by loading a 4-bit value

for N (The default value for N is 8)

TABLE 4-5 Head Settle Time Calculation

Data Rate

Multiplier

Head Settle

(kbps)

(4 Bit Value)

Time (ms)

250

N c 8

0 – 120

300

N c 6666

0 – 100

500

N c 4

0–60

1000

N c 2

0–30

Read Gate Diagnostic

0 e Enable DSKCHG disk interface input for normal

operation

1 e

Enable DSKCHG to act as an external Read Gate

input signal to the Data Separator This is intend-

ed as a test mode to aid in evaluation of the Data

Separator

PUMP Pulse Output Diagnostic

0 e Enable MFM output pin for normal operation

1 e

Enable the MFM output to act as the active low

output of the Data Separator charge pump This

signal consists of a series of pulses indicating

when the phase comparator is making a phase

correction This Pump output is active low for a

pump up or pump down signal from the phase

comparator and is intended as a test mode to aid

in the evaluation of the Data Separator

417 NSC Command

The NSC command can be used to distinguish between the

FDC versions and the 82077 The Result Phase byte

uniquely identifies the floppy controller as a PC87306 which

returns a value of 73h The 82077 and DP8473 return a

value of 80h signifying an invalid command The lower four

bits of this result byte are subject to change by National

and reflects the particular version of the floppy disk control-

ler part

Command Phase

00011000

Execution Phase None

Result Phase

01110011

418 Perpendicular Mode Command

The Perpendicular Mode command is designed to support

the unique Format and Write Data requirements of Perpen-

dicular (Vertical) Recording disk drives (4 Mbyte unformat-

ted capacity) The Perpendicular Mode command config-

ures each of the four logical drives as a perpendicular or

conventional disk drive Configuration of the four logical disk

drives is done via the D3 – 0 bits or with the GAP and WG

control bits This command should be issued during the ini-

tialization of the floppy controller

Command Phase

0100

DC3

DC2

DC1

DC0

GAP

Execution Phase

Internal registers are written

Result Phase

None

Perpendicular Recording drives operate in ‘‘Extra High Den-

sity’’ mode at 1 Mbps and are downward compatible with

144 Mbyte and 720 kbyte drives at 500 kbps (High Density)

and 250 kbps (Double Density) respectively If perpendicular

drives are present in the system this command should be

issued during initialization of the floppy controller which

configures each drive as perpendicular or conventional

Then when a drive is accessed for a Format or Write Data

command the floppy controller adjusts the Format or Write

Data parameters based on the data rate selected (see Ta-

ble 4-6)

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