AM79C970 datasheet(63/168 Pages) AMD

63 / 168 page

AMD

P R E L I M I N A R Y

1-930

Am79C970

Software may invoke DWIO mode by performing a Dou-

ble Word write access to the I/O location at offset 10h

(RDP). Note that 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.

1-, 2- and 3-byte accesses to PCnet-PCI controller I/O

resources are not allowed during DWIO mode.

The mapping of the PCnet-PCI controller resources into

the 32-byte I/O space varies depending upon the setting

of the DWIO bit of BCR18. Depending upon the setting

of this variable, the 32-byte I/O space will be either Word

I/O mapped (WIO) or Double Word I/O mapped (DWIO).

A DWIO setting of 0 produces Word I/O mode, while a

DWIO setting of 1 produces Double Word I/O mapping.

DWIO is automatically programmed as active when the

system attempts a DWORD write access to offset 10h of

the PCnet-PCI controller I/O space. The power up reset

value of DWIO will be ZERO, and this value will be main-

tained until a DWORD access is performed to PCnet-

PCI controller I/O space.

Therefore, if DWIO mode is desired, it is imperative that

the first access to the PCnet-PCI controller be a

DWORD write access to offset 10h.

Alternatively, if DWIO mode is not desired, then it is im-

perative that the software never executes a DWORD

write access to offset 10h of the PCnet-PCI controller

I/O space.

Once the DWIO bit has been set to a ONE, only a hard-

ware H_RESET can reset it to a ZERO.

The DWIO mode setting is unaffected by the S_RESET

or setting the STOP bit.

WIO I/O Resource Map

When the PCnet-PCI controller I/O space is mapped as

Word I/O, then the resources that are allotted to the

PCnet-PCI controller occur on word boundaries that are

offset from the PCnet-PCI controller I/O base address

as shown in the following table:

No. of

Offset

Bytes

APROM

10h

RDP

12h

RAP (shared by RDP and BDP)

14h

Reset Register

16h

BDP

18h

Vendor Specific Word

1Ah

Reserved

1Ch

Reserved

1Eh

Reserved

When PCnet-PCI controller I/O space is Word mapped,

all I/O resources fall on word boundaries and all I/O re-

sources are word quantities. However, while in Word I/O

mode, APROM locations may also be accessed as indi-

vidual bytes either on odd or even byte addresses.

Attempts to write to any PCnet-PCI controller I/O re-

sources

(except to offset 10h, RDP) as 32 bit quantities

while in Word I/O mode are illegal and may cause unex-

pected reprogramming of the PCnet-PCI controller con-

trol registers. Attempts to

read from any PCnet-PCI

controller I/O resources as 32-bit quantities while in

Word

I/O

mode

are

illegal

and

will

yield

undefined values.

An attempt to write to offset 10h (RDP) as a 32 bit quan-

tity while in Word I/O mode will cause the PCnet-PCI

controller to exit WIO mode and immediately thereafter,

to enter DWIO mode.

Word accesses to non word address boundaries are not

allowed while in WIO mode. (A write access may cause

unexpected reprogramming of the PCnet-PCI controller

control registers. A read access will yield undefined

values.)

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 PCnet-PCI controller

control registers; a read access will yield undefined val-

ues.)

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