MDS213 Datasheet, PDF (25/120 Pages) Zarlink Semiconductor Inc – 12-Port 10/100Mbps + 1Gbps Ethernet Switch

MDS213
Data Sheet
If a collision occurs, after the first 64 bytes of data, the MAC/GMAC ceases data transmission and sends the jam
sequence to notify all connected nodes of a collision. This jam sequence will persist for 32 bit times. The jam
sequence is a 32 bit predetermined pattern used to notify other nodes that there is a collision on the network.
If a collision occurs during preamble generation, or within the first 64 bytes, the transmitter waits until the preamble
is completed and then "backs off" (that is, stops transmitting) for a specific period (defined by the IEEE 802.3 Binary
Exponential Backoff Algorithm) before sending the jam sequence and rescheduling transmission. A frame with a
size no less than 96 bits (64 bits of preamble and 32 bits of jam pattern), is sent to guarantee that the duration of the
collision is long enough to be detected by the transmitting ports involved.
3.5 Auto-negotiation
The default value of the MDS213 MAC/GMAC enables Auto-negotiation. The default value is over written if the
PHY lacks the ability to support Auto-negotiation, which is ascertained through its respective management
interface, RMII/GMII. The Auto-negotiation process detects the different modes of operation (i.e. speed selection,
duplex mode) supported by the system at the other end of the link segment. Upon power on/reset, the PHY
generates a special sequence of fast link pulses (FLPs) to begin Auto-negotiation. The MDS213 MAC/GMAC,
supporting Auto-negotiation, reads the results from status register in the PHY (10/100 mode) or in the PCS
submodule (PCS Giga mode).
3.6 VLAN Support
Virtual Local Area Networks (VLANs) assemble a group of independent ports (and/or MAC addresses) to
communicate as if they were on the same physical LAN segment, without being restricted by the physically
connected hardware. The ports are logically grouped together by VLAN Identifiers (VLAN IDs). The MDS213
implements a MAC Address-based classification that associates each VLAN ID with its MAC address in the Switch
Database Memory (SDM) for purposes of aging out, or replacing, old VLANs.
The MDS213 MAC/GMAC recognizes VLAN-Tagged frame formats. During transmission, the MAC/GMAC inserts
(or extracts) the 4-byte VLAN Tag and regenerates the Frame Check Sequence for the transmitted frame. VLAN
support requires an increase in the maximum legal frame size, which is set in the Device Configuration Register
(DCR2), from 1518 to 1522 bytes. During transmission, if the MAC/GMAC is required to remove the VLAN Tag from
a 64-67 byte Rx frame, the MAC/GMAC will append extra bytes (pad) to form a 64 byte frame.
3.7 MAC Control Frames
MAC Control Frames, as defined by the IEEE, are used for specific control functions within the MAC Control
sublayer "MAC Control." Similar to data frames, control frames are also encapsulated by the CSMA/CD MAC,
meaning that they are prepended by a Preamble and Start of Frame delimiter and appended by a Frame Check
Sequence. These frames may be distinguished from other MAC frames by their length/type field identifier (88.08h).
The control functions are distinguished by an opcode contained in the first two bytes of the frame. Upon receipt,
MAC control parses the incoming frame and determines, by looking at the opcode and the MAC address, whether it
is destined for the MAC (a data frame) or for a specific function within MAC Control. After performing the specified
functions, the MDS213 discards all MAC control frames it receives, regardless of the port configuration. These
control frames are not forwarded to any other port and are not used to learn source addresses.
3.8 Flow Control
Flow control reduces the risk of data loss in the event a long burst of activity causes the MDS213 to saturate the
buffer memory with backlogged frames. The MDS213 supports two types of Flow Control: Collision-based for half-
duplex mode and IEEE 802.3x Flow Control for full duplex mode. In both cases, the MDS213 recognizes
congestion by constantly monitoring available frame buffer memory. When the amount of free buffer space has
been depleted, the MDS213 initiates the flow control mechanism appropriate to the current mode of operation.
Setting the Flow Control (FC_Enable) bit in the MAC Port Configuration Register (ERC1) turns this operation on,
thereby initiating PAUSE frames or applying backpressure flow control when necessary
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