AM79C976 datasheet(210/309 Pages) AMD

210 / 309 page

210

Am79C976

8/01/00

P R E L I M INARY

read operation of the EEPROM

through the interface. The EE-

PROM data that is fetched during

the read will be stored in the ap-

propriate internal registers on

board the Am79C976 controller.

Upon completion of the EEPROM

read operation, the Am79C976

controller will assert the PVALID

bit. EEPROM contents will be in-

directly accessible to the host

through read accesses to the Ad-

dress PROM (offsets 0h through

Fh) and through read accesses to

other EEPROM programmable

registers. Note that read access-

es from these locations will not

actually access the EEPROM it-

self, but instead will access the

Am79C976 controller’s internal

copy of the EEPROM contents.

Write accesses to these locations

may change the Am79C976 con-

troller register contents, but the

EEPROM locations will not be af-

fected. EEPROM locations may

be accessed directly through

BCR19.

At the end of the sequential read

operation, the PREAD bit will au-

tomatically be reset to a 0 by the

Am79C976

controller

and

PVALID will be set, provided that

an EEPROM existed on the inter-

face pins and that the checksum

for the EEPROM contents was

correct.

Note that when PREAD is set to a

1, then the Am79C976 controller

will no longer respond to any ac-

cesses directed toward it, until

the PREAD operation has com-

pleted

successfully.

The

Am79C976 controller will termi-

nate these accesses with the as-

sertion of DEVSEL and STOP

while TRDY is not asserted, sig-

naling to the initiator to discon-

nect and retry the access at a

later time.

If a PREAD command is given to

the Am79C976 controller but no

EEPROM is attached to the inter-

face pins, the PREAD bit will be

cleared to a 0, and the PVALID bit

will remain reset with a value of 0.

This applies to the automatic, se-

quential read of the EEPROM af-

ter H_RESET as well as to host

initiated PREAD commands. EE-

PROM programmable locations

on board the Am79C976 control-

ler will be set to their default val-

ues by such an aborted PREAD

operation. For example, if the

aborted PREAD operation imme-

diately followed the H_RESET

operation, then the final state of

the EEPROM programmable lo-

cations will be equal to the

H_RESET

programming

for

those locations.

If a PREAD command is given to

the Am79C976 controller and the

auto-detection pin (EESK/LED1/

SFBD)

indicates

that

EEPROM is present, then the

EEPROM read operation will still

be attempted.

Note that at the end of the

H_RESET operation, a read of

the EEPROM will be performed

automatically. This H_RESET-

generated EEPROM read func-

tion will not proceed if the auto-

detection pin (EESK/LED1) indi-

cates

that

EEPROM

present.

Read/Write accessible. PREAD

is set to 0 during H_RESET and

is unaffected by S_RESET or the

STOP bit.

EEDET

EEPROM Detect. This bit indi-

cates the sampled value of the

EESK/LED1 pin at the end of

H_RESET. This value indicates

whether or not an EEPROM is

present at the EEPROM inter-

face. If this bit is a 1, it indicates

that an EEPROM is present. If

this bit is a 0, it indicates that an

EEPROM is not present.

EEDET is read only; write opera-

tions have no effect. The value of

this bit is determined at the end of

the H_RESET operation. It is un-

affected by S_RESET or the

STOP bit.

AM79C976 Datasheet(PDF) 210 Page - Advanced Micro Devices

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