PC87413 datasheet(59/257 Pages) NSC

59 / 257 page

3.0 Device Architecture and Configuration (Continued)

Revision 1.2

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3.8.3

FDC Configuration Register

This register is reset by hardware to 24h.

Power Well:VDD

Location:Index F0h

Type:

R/W

Bit

76543210

Name

Four-Drive

Encode

Enable

TDR

Mode

DENSEL

Polarity

Control

FDC 2Mbps

Enable

Write

Protect

PC-AT or

PS/2 Drive

Mode Select

Reserved

TRI-STATE

Control

Reset

00100100

Bit

Description

Four-Drive Encode Enable.

0: Two floppy drives are directly controlled by DR1-0, MTR1-0 (default)

1: Four floppy drives are controlled with the aid of an external decoder

TDR Register Mode.

0: PC-AT-Compatible Drive mode; i.e., bits 7-2 of the TDR are 111111b (default)

1: Enhanced Drive mode

DENSEL Polarity Control.

0: Active low for 500 Kbps or 1 or 2 Mbps data rates

1: Active high for 500 Kbps or 1 or 2 Mbps data rates (default)

FDC 2Mbps Enable. This bit is set only when a 2 Mbps drive is used.

0: 2 Mbps disabled and the FDC clock is 24 MHz (default)

1: 2 Mbps enabled and the FDC clock is 48 MHz

Write Protect. This bit enables forcing of write protect functionality by software. When set, writes to the floppy

disk drive are disabled. This effect is identical to an active WP signal.

0: Write protected according to WP signal (default)

1: Write protected regardless of value of WP signal

PC-AT or PS/2 Drive Mode Select.

0: PS/2 Drive mode

1: PC-AT Drive mode (default)

Reserved.

TRI-STATE Control. When enabled and the device is inactive (see Section 3.3.1 on page 43), the logical device

output pins are in TRI-STATE.

0: Disabled (default)

1: Enabled

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