AM79C971VCW Advanced Micro Devices, AM79C971VCW Datasheet - Page 167

• Manufacturer Part Number: AM79C971VCW
• Description: PCnet-FAST Single-Chip Full-Duplex 10/100 Mbps Ethernet Controller for PCI Local Bus
• Manufacturer: Advanced Micro Devices

BCR19: EEPROM Control and Status
Bit
31-16 RES
15
PVALID
Name
Reserved locations. Written as
zeros and read as undefined.
EEPROM Valid status bit. Read
accessible only. PVALID is read
only; write operations have no ef-
fect. A value of 1 in this bit indi-
cates that a PREAD operation
has occurred, and that (1) there is
an EEPROM connected to the
Am79C971 controller interface
pins and (2) the contents read
from the EEPROM have passed
the checksum verification opera-
tion.
A value of 0 in this bit indicates a
failure in reading the EEPROM.
The checksum for the entire 64
bytes of EEPROM is incorrect or
no EEPROM is connected to the
interface pins.
PVALID is set to 0 during
H_RESET and is unaffected by
S_RESET or the STOP bit. How-
ever, following the H_RESET op-
eration, an automatic read of the
EEPROM will be performed. Just
as is true for the normal PREAD
command, at the end of this auto-
matic read operation, the PVALID
bit may be set to 1. Therefore,
H_RESET will set the PVALID bit
to 0 at first, but the automatic EE-
PROM read operation may later
set PVALID to a 1.
If PVALID becomes 0 following
an EEPROM read operation (ei-
ther automatically generated af-
ter
through PREAD), then all EE-
PROM-programmable BCR loca-
tions will be reset to their
H_RESET values. The content of
the Address PROM locations,
however, will not be cleared.
If no EEPROM is present at the
EESK, EEDI, and EEDO pins,
then all attempted PREAD com-
mands will terminate early and
PVALID will not be set. This ap-
plies to the automatic read of the
Description
H_RESET,
or
P R E L I M I N A R Y
requested
Am79C971
14
PREAD
EEPROM after H_RESET, as
well as to host-initiated PREAD
commands.
EEPROM Read command bit.
When this bit is set to a 1 by the
host, the PVALID bit (BCR19, bit
15) will immediately be reset to a
0, and then the Am79C971 con-
troller will perform a read opera-
tion
EEPROM through the interface.
The
fetched during the read will be
stored in the appropriate internal
registers
Am79C971 controller. Upon com-
pletion of the EEPROM read op-
eration, the Am79C971 controller
will assert the PVALID bit. EE-
PROM contents will be indirectly
accessible to the host through
read accesses to the Address
PROM (offsets 0h through Oh)
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
Am79C971 controllers internal
copy of the EEPROM contents.
Write accesses to these locations
may change the Am79C971 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 read operation,
the PREAD bit will automatically
be reset to a 0 by the Am79C971
controller and PVALID will bet
set, provided that an EEPROM
existed on the interface pins and
that the checksum for the entire
64 bytes of EEPROM was cor-
rect.
Note that when PREAD is set to a
1, then the Am79C971 controller
will no longer respond to any ac-
cesses directed toward it, until
the PREAD operation has com-
pleted
Am79C971 controller will termi-
nate these accesses with the as-
of
EEPROM
64
successfully.
on
bytes
data
board
from
that
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