AM79C976KI AMD (ADVANCED MICRO DEVICES), AM79C976KI Datasheet - Page 84

• Manufacturer Part Number: AM79C976KI
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of AM79C976KI

• Operating Supply Voltage (typ): 3.3V
• Operating Supply Voltage (min): 2.97V
• Operating Supply Voltage (max): 3.63V
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 208
• Lead Free Status / RoHS Status: Not Compliant

The receive process starts when RX_DV is asserted.
RX_DV must remain asserted until the end of the re-
ceive frame. If the external PHY device detects errors
in the currently received frame, it asserts the RX_ER
signal. RX_ER can be used to signal special conditions
out of band when RX_DV is not asserted. Two defined
out-of-band conditions for this are the 100BASE-TX
signaling of bad Start of Frame Delimiter and the
100BASE-T4 indication of illegal code group before the
receiver has synchronized with the incoming data. The
Am79C976 controller will not respond to these condi-
tions. All out of band conditions are currently treated as
NULL events. Certain in-band non-IEEE 802.3-compli-
ant flow control sequences may cause erratic behavior
for the Am79C976 controller. Consult the switch/
bridge/router/hub manual to disable the in-band flow
control sequences if they are being used.
MII Network Status Interface
The MII also provides the CRS (Carrier Sense) and
COL (Collision Sense) signals that are required for
IEEE 802.3 operation. Carrier Sense is used to detect
non-idle activity on the network for the purpose of inter-
frame spacing timing in half-duplex mode. Collision
Sense is used to indicate that simultaneous transmis-
sion has occurred in a half-duplex network.
MII Management Interface
The MII provides a two-wire management interface so
that the Am79C976 controller can control external PHY
devices and receive status from them.
The Am79C976 controller offers direct hardware sup-
port of the external PHY device without software inter-
vention. The device automatically uses the MII
Management Interface to read auto-negotiation infor-
mation from the external PHY device and configures
84
Figure 33. Media Independent Interface
Am79C976
P R E L I M I N A R Y
Am79C976
the MAC accordingly. The controller also provides the
host CPU indirect access to the external PHY through
the MII Control, Address, and Data registers (BCR32,
33, 34).
With software support the Am79C976 controller can
support up to 31 external PHYs attached to the MII
Management Interface.
Two independent state machines use the MII Manage-
ment Interface to poll external PHY devices: the Net-
work Port Manager and the Auto-poll State Machine.
The Network Port Manager coordinates the auto-nego-
tiation process, while the Auto-poll State Machine inter-
rupts the host CPU when it detects changes in user-
selected PHY registers.
The Network Port Manager sends a management
frame to the default PHY about once every 900 ms to
determine auto-negotiation results and the current link
status. The Network Port Manager uses the auto-nego-
tiation results to set the MAC’s speed, duplex mode,
and flow control ability. Changes detected by the Net-
work Port Manager affect the operation of the MAC and
MIB counters. For example, if link failure is detected,
the transmitter will increment the XmtLossCarrier
counter each time it attempts to transmit a frame.
The Auto-poll State Machine periodically sends man-
agement frames to poll the status register of the default
PHY device plus up to 5 user-selected PHY registers
and interrupts the host processor if it detects a change
in any of these registers. The Auto-poll State Machine
does not change the state of the MAC engine.
MII Management Frames
The format of an MII Management Frame is defined in
Clause 22 of IEEE Std 802.3. The start of an MII Man-
4
4
RXD(3:0)
RX_DV
RX_ER
RX_CLK
CRS
COL
TXD(3:0)
TX_EN
TX_CLK
MDC
MDIO
Receive Signals
Network Status Signals
Management Port Signals
Transmit Signals
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