AL103 Revision 1.0
3. Functional Description
3.1 Data Reception
The port will go into the receive-state when RX_DV in the MII interface is asserted. The MII
(Media Independent Interface) presents the received data in four-bit nibbles that are synchronous to
the receive clock (25 MHz for 100 Mbit/s or 2.5 MHz for 10 Mbit/s). The AL103 will then attempt
to detect the occurrence of the SFD (Start Frame Delimiter) pattern “10101011.” All preamble data
prior to SFD are discarded. Once SFD is detected from the MII interface, the frame data is
forwarded and stored in the buffer of the switch.
3.1.1 Illegal Frame Length
During the receiving process, the AL103 MAC will monitor the length of the received frame. Legal
Ethernet frames should have a length of no less than 64 bytes and no more than 1536 bytes. Any
frames with illegal frame length are discarded.
3.1.2 Long Frames
The AL103 can handle frame size up to 1536 bytes. All frames longer than 1536 bytes will be
th
discarded. If the port continues to receive data after the 1536 byte, the port’s data will be filtered.
If the port is in half-duplex mode, the port will no longer be able to transmit or receive data during
the long frame reception.
3.1.3 False Carrier Events
If CRS (Carrier Sense) signal in the MII interface is asserted but the receive RX_DV (Receive Data
Valid) signal is not asserted within 16BT (Bit Period), the port is considered to have a false carrier
event.
3.1.4 Frame Filtering
The AL103 will make filtering and forwarding decisions for each frame received based on its frame
routing table, VLAN Mapping, port state, and the system configuration.
Under the following conditions, received frames are filtered:
•
The AL103 will check all received frames for errors such as symbol error, FCS
error, short event, runt, long event, etc. Frames with any kind of error will not be
forwarded to their destination port.
•
•
•
Any frame heading to its own source port will be filtered.
Frames heading to a disabled receiving port will be filtered.
If the input buffer of the port is full, the incoming frame will be discarded. It is
recommended that the flow control be used to prevent any loss of data. If the flow
control option is enabled, this event will not occur. The remote station will
transmit frame when the input buffer becomes available.
•
If the frame has any security violation and the security option is enabled at the
receiving port.
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Reference Only / Allayer Communications
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