PC87332 datasheet(81/98 Pages) NSC

81 / 98 page

80 Integrated Device Electronics Interface (IDE) (Continued)

The two ’LS245 chips are used to enable or TRI-STATE the

data bus signals In the PC-AT mode the PC87332 provides

the two hard disk chip selects (HCS0 HCS1) for the IDE

interface

The HCS0 output is active low when the 1F0 – 1F7h IO

address space is chosen and corresponds to the 1FX signal

on the IDE header

The HCS1 output is active low when the 3F6 or 3F7 IO

addresses are chosen and corresponds to 3FX on the IDE

header These are the two address blocks used in the

PC-AT hard disk controller

Table 8-1 summarizes the addresses used by the PC-AT

hard disk controller

The equations shown in

Figure 8-1 define the signals of the

PC87332 IDE pins

TABLE 8-1 IDE Registers and Their ISA Addresses

Address

Read Function

Write Function

1F0

Data

1F1

Error

Features

(Write Precomp)

1F2

Sector Count

1F3

Sector Number

1F4

Cylinder Low

1F5

Cylinder High

1F6

DriveHead

1F7

Status

Command

3F6

Alternate Status

Device Control

3F7

Drive Address

Not Used

(Note)

Data Bus TRI-STATE

Note

Data bus bit D7 is dedicated to the floppy disk controller at this ad-

dress When reading this address the floppy disk controller disk

change status will be provided by bit D7 There is no write function at

this address in the IDE associated with this bit

Equations

Comments

HCS0 e A9 A8 A7 A6 A5 A4 A3 AEN

Active at 1F0 – 1F7

HCS1 e A9 A8 A7 A6 A5 A4 A3 A2 A1 AEN

Active at 3F6 3F7

IDELO e HCS0 (RD a WR) a HCS1

(WR A0) a RD

Write 1F0 – 1F7 3F6 Read 1F0 – 1F7 3F6 3F7

IDEHI e IOCS16 HCS0 (RD a WR)

Read or Write 1F0 – 1F7 in AT Mode

IDED7 (read) e (HCS0 RD) a (HCS1 A0) RD

Provides D7 during Read 1F0 – 1F7 and 3F6

IDED7 (write) e WR HCS0 a (HCS1 A0)

Provides D7 during Write 1F0 – 1F7 and 3F6

FIGURE 8-1 IDE Interface Signal Equations (Non-DMA)

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