KSZ8851-16MLLU TR Micrel, KSZ8851-16MLLU TR Datasheet - Page 24

• Manufacturer Part Number: KSZ8851-16MLLU TR
• Description: Ethernet ICs Single-Port Ethernet Controller (Automotive Grade)
• Manufacturer: Micrel

Specifications of KSZ8851-16MLLU TR

• Rohs: yes
• Product: Ethernet Controllers
• Package / Case: LQFP-48
• Mounting Style: SMD/SMT

flow control is based on availability of the system resources.
There are three programmable low watermark register FCLWR (0xB0), high watermark register FCHWR (0xB2) and
overrun watermark register FCOWR (0xB4) for flow control in RXQ FIFO. The KSZ8851-16MLL will send PAUSE frame
when the RXQ buffer hit the high watermark level (default 3.072KByte available) and stop PAUSE frame when the RXQ
buffer hit the low watermark level (default 5.12KByte available). The KSZ8851-16MLL will drop packet when the RXQ
buffer hit the overrun watermark level (default 256-Byte available).
The KSZ8851-16MLL issues a flow control frame (Xoff, or transmitter off), containing the maximum pause time defined in
IEEE standard 802.3x. Once the resource is freed up, the KSZ8851-16MLL sends out the another flow control frame
(Xon, or 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 KSZ8851-16MLL 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 KSZ8851-16MLL
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 KSZ8851-16MLL 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”.
May 2012
Micrel, Inc.
Item
1
2
3
4
5
6
7
8
9
Hash perfect (Default)
Perfect with Multicast
Inverse hash perfect
Inverse hash only
Multicast address
Filtering Mode
Inverse perfect
Hash only with
Promiscuous
Address
Hash only
Perfect
passed
Receive Control Register (0x74 – 0x75): RXCR1
RX All
(Bit 4)
0
0
0
0
0
0
1
1
1
RX Inverse
(Bit 1)
0
1
0
1
0
1
1
0
0
RX Physical
Address
(Bit 11)
1
1
0
0
1
1
0
0
1
RX Multicast
Address
24
(Bit 8)
1
1
0
0
0
0
0
0
1
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
Description
KSZ8851-16MLL/MLLI
M9999-050112-2.1