KSZ8842-MQL Datasheet, PDF (48/141 Pages) Micrel Semiconductor – 2-Port Ethernet Switch with Non-PCI Interface

Micrel, Inc.
KSZ8842-16/32 MQL/MVL/MVLI/MBL
For egress rate limiting, the Leaky Bucket algorithm is applied to each output priority queue for shaping output traffic. Inter
frame gap is stretched on a per frame base to generate smooth, non-burst egress traffic. The throughput of each output
priority queue is limited by the egress rate specified.
If any egress queue receives more traffic than the specified egress rate throughput, packets may be accumulated in the
output queue and packet memory. After the memory of the queue or the port is used up, packet dropping or flow control
will be triggered. As a result of congestion, the actual egress rate may be dominated by flow control/dropping at the
ingress end, and may be therefore slightly less than the specified egress rate.
To reduce congestion, it is a good practice to make sure the egress bandwidth exceeds the ingress bandwidth.
MAC Filtering Function
Use the static table to assign a dedicated MAC address to a specific port. When a unicast MAC address is not recorded in
the static table, it is also not learned in the dynamic MAC table. The KSZ8842M includes an option that can filter or
forward unicast packets for an unknown MAC address. This option is enabled by SGCR7[7].
The unicast MAC address filtering function is useful in preventing the broadcast of unicast packets that could degrade the
quality of this port in applications such as voice over Internet Protocol (VoIP).
Configuration Interface
The KSZ8842M operates only as a managed switch.
EEPROM Interface
It is optional in the KSZ8842M to use an external EEPROM. In the case that an EEPROM is not used, the EEEN pin must
be tied Low or floating.
The external serial EEPROM with a standard microwire bus interface is used for non-volatile storage of information such
as the host MAC address, base address, and default configuration settings. The KSZ8842M can detect if the EEPROM is
a 1KB (93C46) or 4KB (93C66) EEPROM device (the 93C46 and the 93C66 are typical EEPROM devices). The
EEPROM is organized as 16-bit mode.
If the EEEN pin is pulled high, the KSZ8842M performs an automatic read of the external EEPROM words 0H to 6H after
the de-assertion of Reset. The EEPROM values are placed in certain host-accessible registers. EEPROM read/write
functions can also be performed by software read/writes to the EEPCR registers.
The KSZ8842M EEPROM format is given below.
WORD
15
87
0
0H
Base Address
1H
Host MAC Address Byte 2
Host MAC Address Byte 1
2H
Host MAC Address Byte 4
Host MAC Address Byte 3
3H
Host MAC Address Byte 6
Host MAC Address Byte 5
4H
Reserved
5H
Reserved
6H
ConfigParam (see Table 13)
7H-3FH
Not used for KSZ8842M (available for user to use)
Table 12. EEPROM Format
October 2007
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M9999-102207-1.9