FDC37C78 datasheet(7/82 Pages) MICROCHIP

7 / 82 page

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

BUFFER

TYPE

DESCRIPTION

Reset

RESET

This active high signal resets the chip and

must be valid for 500 ns minimum. The effect

on the internal registers is described in the

appropriate

section.

The

configuration

registers are not affected by this reset.

FLOPPY DISK INTERFACE

Read Disk Data

nRDATA

Raw serial bit stream from the disk drive, low

active.

Each falling edge represents a flux

transition of the encoded data.

Write

Data

nWDATA

OD20

This active low high current driver provides

the encoded data to the disk drive.

Each

falling edge causes a flux transition on the

media.

Head

Select

nHDSEL

OD20

This high current output selects the floppy

disk side for reading or writing. A logic "1" on

this pin means side 0 will be accessed, while

logic "0" means side 1 will be accessed.

Direction

Control

nDIR

OD20

This high current low active output determines

the direction of the head movement. A logic

"1" on this pin means outward motion, while a

logic "0" means inward motion.

Step Pulse

nSTEP

OD20

This active low high current driver issues a

low pulse for each track-to-track movement of

the head.

Disk Change

nDSKCHG

This input senses that the drive door is open

that

the

diskette

has

possibly been

changed since the last drive selection. This

input is inverted and read via bit 7 of I/O

address 3F7H.

22,

DRVDEN 0,

DRVDEN 1

DRVDEN0,

DRVDEN1

OD20

Indicates the drive and media selected. Refer

configuration

registers

CR03,

CR0B,

CR1F.

Density Select

DENSEL

OD20

Indicates whether a low (250/300 Kb/s) or

high (500 Kb/s) data rate has been selected.

This is determined by the IDENT bit in

Configuration Register 3.

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