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10.6 Address Decoding

The host addresses the drive using programmed I/O. be placed on the three host address lines, DA2 - DA0. strode (-DIOR / -DIOW) shall be given to the chip.

In this method, the required register address should An appropriate chip is selected and a read or write

The following I/O map shows definitions of all the register addresses and functions for these I/O locations. The descriptions of each register are shown in the next paragraph.

Table 10.6-1 Register map

 

Address

 

 

 

 

- CS0

- CS1

HA2

HA1

HA0

READ REGISTER

WRITE REGISTER

0

0

X

X

X

Invalid address

Invalid address

0

1

0

0

0

Data register

Data register

0

1

0

0

1

Error register

Features (Write precompensation)

 

 

 

 

 

 

register

0

1

0

1

0

Sector count

Sector count

0

1

0

1

1

Sector number / LBA bit 0- 7

Sector number / LBA bit0-7

0

1

1

0

0

Cylinder low / LBA bit 8- 15

Cylinder low / LBA bit8-15

0

1

1

0

1

Cylinder high / LBA bit16- 23

Cylinder high / LBA bit16-23

0

1

1

1

0

Device head register

Device head register

 

 

 

 

 

/ LBA bit 24- 27

/ LBA bit 24-27

0

1

1

1

1

Status register

Command register

1

0

0

X

X

High impedance

Not used

1

0

1

0

X

High impedance

Not used

1

0

1

1

0

Alt. status register

Device control register

1

0

1

1

1

Device address register1

Not used

1

1

X

X

X

High impedance

Not used

“X” means “don't care”.

The host generates selection of two independent chips on the interface. The selected high order

chip ,-HOST CS1, is valid only when the host is accessing the address of alternate status register, digital output register , and digital input register respectively. The low order chip, HOST CS0, is used to address all other registers.

The following table shows the standard decode logic to connect with ISA (Industry Standard Architecture) bus .

 

Table 10.6-2 Decode Logic

 

 

Register Address Map

Decode

1F0-1F7

- CS0 = - ((- A9) (-A3)*(- AEN))

3F6,3F7

- CS1= -

 

(A9*A8*A7*A6*A5*A*A8*A7*A6*A5*A4*4)*(-A3)*(-

 

AEN)

170-177

- CS0= - ((- A9)*A8*(- A7)*A6*A5*A4*(- A3)*(- AEN)

376,377

- CS1= - (A9*A8*(- A7)*A6*A5*A4)*(- A3)*(- AEN)

The host data buses 15-8 are valid only when - IOCS16 is active.

•- IOCS16 is asserted when interface address lines match to data register address.

1ATA-2 Notes: This register is obsolete. A device is not supposed to respond to a read of this address. If a device does respond, it shall be sure not to drive the DD7 signal to prevent possible conflict with floppy disk implementations.

The drive supports this register to maintain compatibility for ATA-1.

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