AM79C973BKC\W AMD (ADVANCED MICRO DEVICES), AM79C973BKC\W Datasheet - Page 78

• Manufacturer Part Number: AM79C973BKC\W
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of AM79C973BKC\W

• Operating Supply Voltage (typ): 3.3V
• Operating Supply Voltage (min): 3/3.135V
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 160
• Lead Free Status / RoHS Status: Not Compliant

Host related receive exception conditions include
MISS, BUFF, and OFLO. These are described in the
section, Buffer Management Unit.
Loopback Operation
Loopback is a mode of operation intended for system
diagnostics. In this mode, the transmitter and receiver
are both operating at the same time so that the control-
ler receives its own transmissions. The controller pro-
vides two basic types of loopback. In internal loopback
mode, the transmitted data is looped back to the re-
ceiver inside the controller without actually transmitting
any data to the external network. The receiver will
move the received data to the next receive buffer,
where it can be examined by software. Alternatively, in
external loopback mode, data can be transmitted to
and received from the external network.
Refer to Table 21 for various bit settings required for
Loopback modes.
The external loopback requires a two-step operation.
The internal PHY must be placed into a loopback mode
by writing to the PHY Control Register (BCR33,
BCR34). Then, the Am79C973/Am79C975 controller
must be placed into an external loopback mode by set-
ting the Loop bits.
Miscellaneous Loopback Features
All transmit and receive function programming, such as
automatic transmit padding and receive pad stripping,
operates identically in loopback as in normal operation.
Runt Packet Accept is internally enabled (RPA bit in
CSR124 is not affected) when any loopback mode is in-
voked. This is to be backwards compatible to the C-
LANCE (Am79C90) software.
Since the Am79C973/Am79C975 controller has two
FCS generators, there are no more restrictions on FCS
generation or checking, or on testing multicast address
detection as they exist in the half-duplex PCnet family
devices and in the C-LANCE. On receive, the
Am79C973/Am79C975 controller now provides true
FCS status. The descriptor for a frame with an FCS
error will have the FCS bit (RMD1, bit 27) set to 1. The
FCS generator on the transmit side can still be disabled
by setting DXMTFCS (CSR15,
In internal loopback operation, the Am79C973/
Am79C975 controller provides a special mode to test
the collision logic. When FCOLL (CSR15, bit 4) is set
to 1, a collision is forced during every transmission at-
tempt. This will result in a Retry error.
78
FCS errors
Late collision
bit 3) to 1.
P R E L I M I N A R Y
Am79C973/Am79C975
Full-Duplex Operation
The Am79C973/Am79C975 controller supports full-du-
plex operation on both network interfaces. Full-duplex
operation allows simultaneous transmit and receive ac-
tivity. Full-duplex operation is enabled by the FDEN bit
located in BCR9. Full-duplex operation is also enabled
through Auto-Negotiation when DANAS (BCR 32, bit 7)
is not enabled and the ASEL bit is set, and its link partner
is capable of Auto-Negotiation and full-duplex opera-
tion.
When operating in full-duplex mode, the following
changes to the device operation are made:
Bus Interface/Buffer Management Unit changes:
The MAC engine changes for full-duplex operation are
as follows:
The internal PHY changes for full-duplex operation are
as follows:
The first 64 bytes of every transmit frame are not
preserved in the Transmit FIFO during transmission
of the first 512 bits as described in the Transmit Ex-
ception Conditions section. Instead, when full-du-
plex mode is active and a frame is being transmitted,
the XMTFW bits (CSR80, bits 9-8) always govern
when transmit DMA is requested.
Successful reception of the first 64 bytes of every
receive frame is not a requirement for Receive DMA
to begin as described in the Receive Exception Con-
ditions section. Instead, receive DMA will be re-
quested as soon as either the RCVFW threshold
(CSR80, bits 12-13) is reached or a complete valid
receive frame is detected, regardless of length. This
Receive FIFO operation is identical to when the RPA
bit (CSR124, bit 3) is set during half-duplex mode
operation.
Changes to the Transmit Deferral mechanism:
— Transmission is not deferred while receive is
— The IPG counter which governs transmit deferral
The 4.0 µs carrier sense blinding period after a
transmission during which the SQE test normally
occurs is disabled.
The collision indication input to the MAC engine is
ignored.
The collision detect (COL) pin is disabled.
The SQE test function is disabled (10 Mbps).
Loss of Carrier (LCAR) reporting is disabled.
active.
during the IPG between back-to-back transmits
is started when transmit activity for the first
packet ends, instead of when transmit and car-
rier activity ends.