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2. FDSE (Full Duplex Switched Ethernet).
Enabled by FDSE bit in TCR bit. When the
SMC91C95 is configured for FDSE, its
transmit and receive paths will operate
independently and some CSMA/CD
functions are disabled such as Carrier
Sense.
Behavior in FDSE Mode
The main 802.3 section affected by FDSE is
4.2.8 where the Frame Transmission procedural
model is presented. The changes are:
1. No deferral - The transmit channel is
dedicated and always available - The
device will transmit whenever it has a
packet ready to be sent, while respecting
the interframe spacing between transmit
packets.
2. No collision detection - There are no
collisions in a switched environment.
The EPH implementation of the procedural
model uses as ‘collisionDetect’ the MAC
collision input, sourced from the 10BASE-
T front end, AUI front end, or External
Endec interface. This collision input is
observed by the Transmit State Machine
while ‘transmitting’ is true, that is during
Preamble, Data, Pad, and CRC states. If
collision is active during any of these states
the state machine transitions to JAM and
BACKOFF states.
3. 10BASE-T loopback - Typically 10BASE-T
drivers are internally looped back to the
differential receivers.
“Magic Packet” Support
If the WAKEUP_EN bit in the Control Register
(Bank1, Offset C) is set, the controller will come
out of any powerdown mode. If this bit is not
set, this functionality is disabled.
When a “Magic Packet” is received, the ethernet
controller will generate an interrupt causing the
host to initiate a service routine to find the
source of the event. The Interrupt bit in the
ECSR is also set if the host plans on polling the
controller for Wakeup status.