AM79C978VCSLASHW datasheet(97/261 Pages) AMD

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Am79C978

Double Word I/O Mode

The Am79C978 controller can be configured to operate

in DWord (32-bit) I/O mode. The software can invoke

the DWIO mode by performing a DWord write access

to the I/O location at offset 10h (RDP). The data of the

write access must be such that it does not affect the in-

tended operation of the Am79C978 controller. Setting

the device into 32-bit I/O mode is usually the first oper-

ation after H_RESET or S_RESET. The RAP register

will point to CSR0 at that time. Writing a value of 0 to

CSR0 is a safe operation. DWIO (BCR18, bit 7) will be

set to 1 as an indication that the Am79C978 controller

operates in 32-bit I/O mode.

Note: Even though the I/O resource mapping changes

when the I/O mode setting changes, the RDP location

offset is the same for both modes. Once the DWIO bit

has been set to 1, only H_RESET can clear it to 0. The

DWIO mode setting is unaffected by S_RESET or set-

ting of the STOP bit. Table 27 shows how the 32 bytes

of address space are used in DWord I/O mode.

All I/O resources must be accessed in DWord quanti-

ties and on DWord addresses. A read access other

than listed in Table 27 will yield undefined data, a write

operation may cause unexpected reprogramming of

the Am79C978 control registers.

Table 25.

I/O Map in Word I/O Mode (DWIO = 0)

Offset

No. of

Bytes

00h - 0Fh

APROM

10h

RDP

12h

RAP (shared by RDP and BDP)

14h

Reset Register

16h

BDP

18h - 1Fh

Reserved

Table 26.

Legal I/O Accesses in Word I/O Mode (DWIO = 0)

AD[4:0]

BE[3:0]

Type

Comment

0XX00

1110

Byte read of APROM location 0h, 4h, 8h, or Ch

0XX01

1101

Byte read of APROM location 1h, 5h, 9h, or Dh

0XX10

1011

Byte read of APROM location 2h, 6h, Ah, or Eh

0XX11

0111

Byte read of APROM location 3h, 7h, Bh, or Fh

0XX00

1100

Word read of APROM locations 1h (MSB) and 0h (LSB), 5h and 4h, 8h and 9h, or

Ch and Dh

0XX10

0011

Word read of APROM locations 3h (MSB) and 2h (LSB), 7h and 6h, Bh and Ah, or

Fh and Eh

10000

1100

Word read of RDP

10010

0011

Word read of RAP

10100

1100

Word read of Reset Register

10110

0011

Word read of BDP

0XX00

1100

Word write to APROM locations 1h (MSB) and 0h (LSB), 5h and 4h, 8h and 9h, or

Ch and Dh

0XX10

0011

Word write to APROM locations 3h (MSB) and 2h (LSB), 7h and 6h, Bh and Ah, or

Fh and Eh

10000

1100

Word write to RDP

10010

0011

Word write to RAP

10100

1100

Word write to Reset Register

10110

0011

Word write to BDP

10000

0000

DWord write to RDP,

switches device to DWord I/O mode

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