KSZ8851SNLI Micrel Inc, KSZ8851SNLI Datasheet - Page 21

• Manufacturer Part Number: KSZ8851SNLI
• Manufacturer: Micrel Inc

Specifications of KSZ8851SNLI

• Operating Supply Voltage (typ): 3.3V
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 32
• Lead Free Status / RoHS Status: Supplier Unconfirmed

Note 1: Bit 0 (RX Enable), Bit 5 (RX Unicast Enable) and Bit 6 (RX Multicast Enable) must set to 1 in RXCR1 register.
Note 2: The KSZ8851SNL will discard frame with SA same as the MAC address if bit[0] is set in RXCR2 register.
transmitter on) with zero pause time to turn off the flow control (turn on transmission to the port). A hysteresis feature is
provided to prevent the flow control mechanism from being constantly activated and deactivated.
Half-Duplex Backpressure
A half-duplex backpressure option (non-IEEE 802.3 standards) is also provided. The activation and deactivation
conditions are the same as in full-duplex mode. If backpressure is required, the KSZ8851SNL sends preambles to defer
the other stations' transmission (carrier sense deference).
To avoid jabber and excessive deference (as defined in the 802.3 standard), after a certain time, the KSZ8851SNL
discontinues the carrier sense and then raises it again quickly. This short silent time (no carrier sense) prevents other
stations from sending out packets thus keeping other stations in a carrier sense deferred state. If the port has packets to
send during a backpressure situation, the carrier sense type backpressure is interrupted and those packets are
transmitted instead. If there are no additional packets to send, carrier sense type backpressure is reactivated again until
chip resources free up. If a collision occurs, the binary exponential back-off algorithm is skipped and carrier sense is
generated immediately, thus reducing the chance of further collision and carrier sense is maintained to prevent packet
reception.
Address Filtering Function
The KSZ8851SNL supports 11 different address filtering schemes as shown in the following Table 3. The Ethernet
destination address (DA) field inside the packet is the first 6-byte field which uses to compare with either the host MAC
address registers (0x10 – 0x15) or the MAC address hash table registers (0xA0 – 0xA7) for address filtering operation.
The first bit (bit 40) of the destination address (DA) in the Ethernet packet decides whether this is a physical address if bit
40 is “0” or a multicast address if bit 40 is “1”.
August 2009
Item
Micrel, Inc.
10
11
1
2
3
4
5
6
7
8
9
Address Filtering
Inverse hash only
Multicast address
Multicast address
Physical address
Physical address
Inverse perfect
Hash only with
Hash only with
Inverse hash
Promiscuous
Hash perfect
Perfect with
Perfect with
Hash only
(Default)
Perfect
passed
passed
passed
passed
perfect
Mode
RX All
(Bit 4)
Receive Control Register (0x74 – 0x75): RXCR1
0
0
0
0
0
0
1
1
1
1
1
RX Inverse
(Bit 1)
0
1
0
1
0
1
1
0
0
0
0
RX Physical
(Bit 11)
Address
Table 3. Address Filtering Scheme
1
1
0
0
1
1
0
0
1
1
0
RX Multicast
Address
(Bit 8)
1
1
0
0
0
0
0
0
1
0
1
21
All Rx frames are passed only if the DA exactly matches the
MAC address in MARL, MARM and MARH registers.
All Rx frames are passed if the DA is not matching the MAC
address in MARL, MARM and MARH registers.
All Rx frames with either multicast or physical destination
address are filtering against the MAC address hash table.
All Rx frames with either multicast or physical destination
address are filtering not against the MAC address hash table.
All Rx frames which are filtering out at item 3 (Hash only) only
are passed in this mode.
All Rx frames are passed with Physical address (DA) matching
the MAC address and to enable receive multicast frames that
pass the hash table when Multicast address is matching the
MAC address hash table.
All Rx frames which are filtering out at item 5 (Hash perfect) only
are passed in this mode.
All Rx frames are passed without any conditions.
All Rx frames are passed with Physical address (DA) matching
the MAC address hash table and with Multicast address without
any conditions.
All Rx frames are passed with Physical address (DA) matching
the MAC address and with Multicast address without any
conditions.
All Rx frames are passed with Multicast address matching the
MAC address hash table and with Physical address without any
conditions.
All Rx frames are passed with Multicast address matching the
MAC address and with Physical address without any conditions.
Description
KSZ8851SNL/SNLI
M9999-083109-2.0