AM79C974 datasheet(61/153 Pages) AMD

61 / 153 page

P R E L I M I N A R Y

AMD

Am79C974

Accesses of non word quantities to any I/O resource are

not allowed while in WIO mode, with the exception of a

read to APROM locations. (A write access may cause

unexpected reprogramming of the Ethernet controller

control registers; a read access will yield undefined

values.)

The Vendor Specific Word (VSW) is not implemented by

the Ethernet controller. This particular I/O address is re-

served for customer use and will not be used by future

AMD Ethernet controller products.

DWIO I/O Resource Map

When the Ethernet controller I/O space is mapped as

Double Word I/O, then all of the resources that are allot-

ted to the Ethernet controller occur on DWORD bounda-

ries that are offset from the Ethernet controller I/O base

address as shown in the table below:

No. of

Offset

Bytes

APROM

10h

RDP

14h

RAP (shared by RDP and BDP)

18h

Reset Register

1Ch

BDP

When Ethernet I/O space is Double Word mapped, all

I/O resources fall on DWORD boundaries. APROM re-

sources are DWORD quantities in DWIO mode. RDP,

RAP and BDP contain only two bytes of valid data; the

other two bytes of these resources are reserved for fu-

ture use. (Note that CSR88 is an exception to this rule.)

The reserved bits must be written as ZEROs, and when

read, are considered undefined.

Accesses to non-doubleword address boundaries are

not allowed while in DWIO mode. (A write access may

cause unexpected reprogramming of the Ethernet con-

troller control registers; a read access will yield unde-

fined values.)

Accesses of less than 4 bytes to any I/O resource are

not allowed while in DWIO mode. (A write access may

cause unexpected reprogramming of the Ethernet con-

troller control registers; a read access will yield unde-

fined values.)

If an EEPROM is not used to program the value of

DWIO, then a DWORD write access to the RDP offset of

10h will automatically program DWIO mode.

Note that in all cases when I/O resource width is defined

as 32 bits, the upper 16 bits of the I/O resource is

reserved and written as ZEROS and read as undefined,

except for the APROM locations and CSR88.

DWIO mode is exited by asserting the

RST pin or by

forcing a re-read of the EEPROM when the EEPROM

will program a ZERO into the DWIO bit location of

BCR10. Assertion of S_RESET or setting the STOP bit

of CSR0 will have no effect on the DWIO mode setting.

I/O Space Comments

The following statements apply to both WIO and DWIO

mapping:

The RAP is shared by the RDP and the BDP.

The Ethernet controller does not respond to any ad-

dresses outside of the offset range 0h–17h when DWIO

= 0 or 0h–1Fh when DWIO = 1. I/O offsets 18h through

1Fh are not used by the Ethernet controller when pro-

grammed for DWIO = 0 mode; locations 1Ah through

1Fh are reserved for future AMD use and therefore

should not be implemented by the user if upward com-

patibility to future AMD devices is desired.

Note that APROM accesses do not directly access the

EEPROM, but are redirected to a set of shadow regis-

ters on board the Ethernet controller that contain a copy

of the EEPROM contents that was obtained during the

automatic EEPROM read operation that follows the

H_RESET operation.

Am79C974’s Ethernet Controller I/O Base Address

The Ethernet PCI Configuration Space Base Address

controller uses. This register is typically programmed by

the PCI configuration utility after system power-up. The

PCI configuration utility must also set the IOEN bit in the

COMMAND register to enable I/O accesses to the

Ethernet controller.

The contents of the Ethernet I/O Base Address Regis-

ters (BCR16 and BCR17) are ignored.

I/O Register Access

All I/O resources are accessed with similar I/O bus

cycles.

I/O accesses to the Ethernet controller begin with a valid

FRAME signal, the C/BE[3:0] lines signaling an I/O read

or I/O write operation and an address on the AD[31:00]

lines that falls within the I/O space of the Ethernet con-

troller. The Ethernet I/O space will be determined by the

Base Address Register in the PCI Configuration Space.

The Ethernet controller will respond to an access to its

I/O space by asserting the

DEVSEL signal and eventu-

ally, by asserting the

TRDY signal.

Typical I/O access times are 6 or 7 clock cycles.

AM79C974 Datasheet(PDF) 61 Page - Advanced Micro Devices

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