RTL8306SD/RTL8306SDM
Datasheet
7.1.3.5
Force Mode
For UTP without auto-negotiation ability, the operation mode can be forced to half duplex. Half duplex
back pressure flow control can be forced to ‘enabled’ on the RTL8306SD/RTL8306SDM side by pin
GxEnFC/GyEnFC/P4EnFC on a group basis upon reset.
7.1.4.
Address Search, Learning, and Aging
When a packet is received, the RTL8306SD/RTL8306SDM will use the bits of the destination MAC
address to index the 2048-entry lookup table, and at the same time compare the destination MAC address
with the contents of the 16-entry CAM. If the indexed entry is valid, or the CAM comparison is matched,
the received packet will be forwarded to the corresponding destination port. Otherwise, the
RTL8306SD/RTL8306SDM will broadcast the packet. This is the ‘Address Search’.
The RTL8306SD/RTL8306SDM then extracts the specific bits of the source MAC address to index the
2048-entry lookup table. If the entry is not in the table it will record the source MAC address and add
switching information. If this is an occupied entry, it will update the entry with new information. This is
called ‘Learning’. If the indexed location has been occupied by a different MAC address (hash collision),
the new source MAC address will be recorded into the 16-entry CAM. The 16-entry CAM reduces
address hash collisions and improves switching performance.
Address aging is used to keep the contents of the address table correct in a dynamic network topology.
The lookup engine will update the time stamp information of an entry whenever the corresponding source
MAC address appears. An entry will be invalid (aged-out) if its time stamp information is not refreshed
by the address learning process during the aging time period. The aging time of the
RTL8306SD/RTL8306SDM is between 200 and 350 seconds.
6-Port 10/100Mbps Single-Chip Dual MII/RMII Switch Controller
37
Track ID: JATR-1076-21 Rev. 1.1
REALTEK [ Realtek Semiconductor Corp. ]
