LAN9117 Datasheet, PDF (16/114 Pages) SMSC Corporation – HIGH PERFORMANCE SINGLE-CHIP 10/100 NON-PCI ETHERNET CONTROLLER

LAN9117
3.0 FUNCTIONAL DESCRIPTION
3.1 10/100 Ethernet MAC
The Ethernet Media Access controller (MAC) incorporates the essential protocol requirements for operating an Ether-
net/IEEE 802.3-compliant node and provides an interface between the host subsystem and the internal Ethernet PHY.
The MAC can operate in either 100-Mbps or 10-Mbps mode.
The MAC operates in both half-duplex and full-duplex modes. When operating in half-duplex mode, the MAC complies
fully with Section 4 of ISO/IEC 8802-3 (ANSI/IEEE standard) and ANSI/IEEE 802.3 standards. When operating in full-
duplex mode, the MAC complies with IEEE 802.3x full-duplex operation standard.
The MAC provides programmable enhanced features designed to minimize host supervision, bus utilization, and pre-
or post-message processing. These features include the ability to disable retries after a collision, dynamic FCS (Frame
Check Sequence) generation on a frame-by-frame basis, automatic pad field insertion and deletion to enforce minimum
frame size attributes, and automatic retransmission and detection of collision frames.
The MAC can sustain transmission or reception of minimally-sized back-to-back packets at full line speed with an inter-
packet gap (IPG) of 9.6 microseconds for 10 Mbps and 0.96 microseconds for 100 Mbps.
The primary attributes of the MAC Function are:
• Transmit and receive message data encapsulation
• Framing (frame boundary delimitation, frame synchronization)
• Error detection (physical medium transmission errors)
• Media access management
• Medium allocation (collision detection, except in full-duplex operation)
• Contention resolution (collision handling, except in full-duplex operation)
• Flow control during full-duplex mode
• Decoding of control frames (PAUSE command) and disabling the transmitter
• Generation of control frames
• Interface to the internal PHY and optional external PHYl
The transmit and receive data paths are separate within the LAN9117 from the MAC to host interface allowing the high-
est performance, especially in full duplex mode. Payload data as well as transmit and receive status are passed on these
busses.
A third internal bus is used to access the MAC’s “Control and Status Registers” (CSR’s). This bus is also accessible
from the host.
On the backend, the MAC interfaces with the 10/100 PHY through an MII (Media Independent Interface) port, internal
to the LAN9117. In addition, there is an external MII interface supporting optional PHY devices. The MAC CSR's also
provide a mechanism for accessing the PHY’s internal registers through the internal SMI (Serial Management Interface)
bus.
The receive and transmit FIFOs allow increased packet buffer storage to the MAC. The FIFOs are a conduit between
the host interface and the MAC through which all transmitted and received data and status information is passed. Deep
FIFOs allow a high degree of latency tolerance relative to the various transport and OS software stacks reducing and
minimizing overrun conditions. Like the MAC, the FIFOs have separate receive and transmit data paths.
The LAN9117 can store up to 250 Ethernet packets utilizing FIFOs, totaling 16K bytes, with a packet granularity of 4
bytes. This memory is shared by the RX and TX blocks and is configurable in terms of allocation. This depth of buffer
storage minimizes or eliminates receive overruns.
DS00002267A-page 16
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