AM79C973BKD\W AMD (ADVANCED MICRO DEVICES), AM79C973BKD\W Datasheet - Page 272

• Manufacturer Part Number: AM79C973BKD\W
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of AM79C973BKD\W

• Lead Free Status / RoHS Status: Compliant

ager will periodically query the external PHY for active
links.
Automatic Network Selection: External PHY
Auto-Negotiable
This case occurs when the MIIPD (BCR32, bit 14) bit is
1. This indicates that there is an external PHY attached
to Am79C973/Am79C975 controller’s MII. If more than
one external PHY is attached to the MII Management
Interface, then the DANAS (BCR32, bit 7) bit must be
set to 1 and then all configuration control should revert
to software. The Am79C973/Am79C975 controller will
read the MII Status register of the external PHY to de-
termine its status and network capabilities. If the exter-
nal PHY is Auto-Negotiation capable and/or the
XPHYANE (BCR32, bit 5) bit is set to 1, then the
Am79C973/Am79C975 controller will start the external
PHY’s Auto-Negotiation process. The Am79C973/
Am79C975 controller will write to the external PHY’s
Advertisement register with the following conditions
set: turn off the Next Pages support, set the Technology
Ability Field from the external PHY MII Status register
read, and set the Type Selector field to the IEEE 802.3
standard. The Am79C973/Am79C975 controller will
then write to the external PHY’s MII Control register in-
structing the external PHY to negotiate the link. The
Am79C973/Am79C975 controller will poll the external
PHY’s MII Status register until the Auto-Negotiation
Complete bit is set to 1and the Link Status bit is set to
1. The Am79C973/Am79C975 controller will then wait
a specific time and then again read the external PHY’s
MII Status register. If the Am79C973/Am79C975 con-
troller sees that the external PHY’s link is down, it will
try to bring up the external PHY’s link manually as de-
scribed above. A new read of the external PHY’s MII
Status register will be made to see if the link is up. If the
link does not come up as programmed after a specific
time, the Am79C973/Am79C975 controller will fail the
external PHY link and start the process again.
Automatic Network Selection: Force External Reset
If the XPHYRST bit (BCR32, bit 6) is set to 1, then the
flow changes slightly. The Am79C973/Am79C975 con-
troller will write to the external PHY’s MII Control regis-
ter wi th the RE SE T bi t s et to 1 (S e e th e MI I
Management Registers section for the MII register bit
descriptions). This will force a complete reset of the ex-
ternal PHY. The Am79C973/Am79C975 controller after
a specific time will poll the external PHY’s MII Control
register to see if the RESET bit is 0. After the RESET
bit is cleared, then the normal flow continues.
External Address Detection Interface
The EADI is provided to allow external address filtering
and to provide a Receive Frame Tag word for propri-
etary routing information. It is selected by setting the
EADISEL bit in BCR2 to 1. This feature is typically uti-
lized by terminal servers, bridges and/or router prod-
272
P R E L I M I N A R Y
Am79C973/Am79C975
ucts. The EADI interface can be used in conjunction
with external logic to capture the packet destination ad-
dress from the nibble as it arrives at the Am79C973/
Am79C975 controller, to compare the captured ad-
dress with a table of stored addresses or identifiers,
and then to determine whether or not the Am79C973/
Am79C975 controller should accept the packet.
If an address match is detected by comparison with ei-
ther the Physical Address or Logical Address Filter reg-
isters contained within the Am79C973/Am79C975
controller or the frame is of the type 'Broadcast', then
the frame will be accepted regardless of the condition
of EAR. When the EADISEL bit of BCR2 is set to 1 and
the Am79C973/Am79C975 controller is programmed
to promiscuous mode (PROM bit of the Mode Register
is set to 1), then all incoming frames will be accepted,
regardless of any activity on the EAR pin.
Internal address match is disabled when PROM
(CSR15, bit 15) is cleared to 0, DRCVBC (CSR15, bit
14) and DRCVPA (CSR15, bit 13) are set to 1, and the
Logical Address Filter registers (CSR8 to CSR11) are
programmed to all zeros.
When the EADISEL bit of BCR2 is set to 1 and internal
address match is disabled, then all incoming frames
will be accepted by the Am79C973/Am79C975 control-
ler, unless the EAR pin becomes active during the first
64 bytes of the frame (excluding preamble and SFD).
This allows external address lookup logic approxi-
mately 58 byte times after the last destination address
bit is available to generate the EAR signal, assuming
that the Am79C973/Am79C975 controller is not config-
ured to accept runt packets. The EADI logic only sam-
ples EAR from 2 bit times after SFD until 512 bit times
(64 bytes) after SFD. The frame will be accepted if EAR
has not been asserted during this window. In order for
the EAR pin to be functional in full-duplex mode, FDR-
PAD bit (BCR9, bit 2) needs to be set. If Runt Packet
Accept (CSR124, bit 3) is enabled, then the EAR signal
must be generated prior to the 8 bytes received, if
frame rejection is to be guaranteed. Runt packet sizes
could be as short as 12 byte times (assuming 6 bytes
for source address, 2 bytes for length, no data, 4 bytes
for FCS) after the last bit of the destination address is
available. EAR must have a pulse width of at least 110
ns.
The EADI outputs continue to provide data throughout
the reception of a frame. This allows the external logic
to capture frame header information to determine pro-
tocol type, internetworking information, and other use-
ful data.
The EADI interface will operate as long as the STRT bit
in CSR0 is set, even if the receiver and/or transmitter
are disabled by software (DTX and DRX bits in CSR15
are set). This configuration is useful as a semi-power-
down mode in that the Am79C973/Am79C975 control-