AM79C971VCW datasheet(105/265 Pages) AMD

105 / 265 page

Am79C971

105

The DWIO mode can be configured from the EEPROM

or programmed by the software.

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 or a read of

EEPROM can clear it to 0. The DWIO mode setting is

unaffected by setting the STOP bit. Table 24 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 25 will yield undefined data, a write

operation may cause unexpected reprogramming of

the Am79C971 control registers

After H_RESET, the Am79C971 controller is pro-

grammed to operate in Word I/O mode. DWIO (BCR18,

bit 7) will be cleared to 0. It will then be loaded by the

value in the EEPROM. Table 20 shows how the 32

bytes of address space are used in Word I/O mode.

All I/O resources must be accessed in word quantities

and on word addresses. The Address PROM locations

can also be read in byte quantities. The only allowed

DWord operation is a write access to the RDP, which

switches the device to DWord I/O mode. A read access

other than listed in the table below will yield undefined

data, a write operation may cause unexpected repro-

gramming of the Am79C971 control registers. Table 23

shows legal I/O accesses in Word I/O mode

Double Word I/O Mode

The Am79C971 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 Am79C971 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 Am79C971 controller

operates in 32-bit I/O mode.

The DWIO mode can be configured from the EEPROM

or programmed by the software.

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 or a read of

EEPROM can clear it to 0. The DWIO mode setting is

unaffected by setting the STOP bit. Table 24 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 25 will yield undefined data, a write

operation may cause unexpected reprogramming of

the Am79C971 control registers

Table 22.

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

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