High-Performance Single-Chip 10/100 Ethernet Controller with HP Auto-MDIX and Industrial Temperature Support
Datasheet
Chapter 3 Functional Description
3.1
10/100 Ethernet MAC
The Ethernet Media Access controller (MAC) incorporates the essential protocol requirements for
operating an Ethernet/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 interpacket 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.
The transmit and receive data paths are separate within the LAN9218i from the MAC to host interface
allowing the highest 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 which is internal to the LAN9218i. 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 LAN9218i 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.
Revision 1.8 (06-06-07)
22
SMSC LAN9218i
DATASHEET
SMSC [ SMSC CORPORATION ]
