PC87311A datasheet(33/78 Pages) NSC

33 / 78 page

40 FDC Command Set Description (Continued)

R255

Recalibrate Step Pulses The bit will determine the

maximum number of recalibrate step pulses the controller

will issue before terminating with an error Default after a

software reset

0 e 85 maximum recalibrate step pulses If ETR e 1

controller will issue 3925 recalibrate step pulses max-

imum

1 e

255 maximum recalibrate step pulses If ETR e 1

controller will issue 4095 maximum recalibrate step

pulses

DENSEL

Density Select Pin Configuration This two bit val-

ue will configure the Density Select output to one of three

possible modes

The default mode will configure the

DENSEL pin according to the state of the IDENT input pin

after a data rate has been selected That is if IDENT is high

the DENSEL pin is active high for the 500 kbs1 Mbs data

rates If IDENT is low the DENSEL pin is active low for the

500 kbs1 Mbs data rates In addition to these modes the

DENSEL output can be set to always low or always high as

shown in Table 4-2 This will allow the user more flexibility

with new drive types

TABLE 4-2 DENSEL Encoding

Bit 1

Bit 0

DENSEL

Pin Definition

Pin Low

Pin High

Undefined

DEFAULT

TABLE 4-3 DENSEL Default Encoding

Data Rate

DENSEL (default)

IDENT e 1

IDENT e 0

250 kbs

Low

High

300 kbs

Low

High

500 kbs

High

Low

1 Mbs

High

Low

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)

(default)

1 e

Drive output signals configured as 40 mA open-drain

outputs

WLD

Scan Wild Card

0 e An FF (hex) from either the mP or the disk during a

Scan command is interpreted as a wildcard character

that will always match true (default)

1 e

The Scan commands do not recognize FF (hex) as a

wildcard character

Head Settle

Time allowed for readwrite head to settle af-

ter a seek during an Implied Seek operation This is con-

trolled as shown in table in next column by loading a 4-bit

value for N (the default value for N is 8)

Data Rate

Multiplier

Head Settle

kbitss

4 Bits

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 oper-

ation (default)

1 e

Enable DSKCHG to act as an external Read Gate

input signal to the Data Separator This is intended as

a test mode to aid in evaluation of the Data Separa-

tor

PUMP Pulse Output Diagnostic

0 e Enable MFM output pin for normal operation

(default)

1 e

Enable the MFM output to act as the active low out-

put 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 will be active low for a pump up or pump

down signal from the phase comparator and is in-

tended as a test mode to aid in the evaluation of the

Data Separator

427 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 PC87311A12

which returns a value of 72h 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 NSC

and will reflect the particular version of the floppy disk con-

troller part

428 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 Mbytes unformat-

ted capacity) The Perpendicular Mode command will con-

figure 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 – D0 bits or with the GAP and WG

control bits This command should be issued during the ini-

tialization of the floppy controller

Perpendicular Recording drives operate in ‘‘Extra High Den-

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

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

and 250 kbs (Double Density) respectively If perpendicular

drives are present in the system this command should be

issued during initialization of the floppy controller which will

configure each drive as perpendicular or conventional

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

command the floppy controller will adjust the Format or

Write Data parameters based on the data rate (see Table

4-4)

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