KSZ8842-PMBL AM TR Micrel Inc, KSZ8842-PMBL AM TR Datasheet - Page 28

• Manufacturer Part Number: KSZ8842-PMBL AM TR
• Description: 2-Port Ethernet Switch/Repeater + 32-bit/33MHz PCI Bus Interface( )
• Manufacturer: Micrel Inc

Specifications of KSZ8842-PMBL AM TR

• Number Of Primary Switch Ports: 2
• Internal Memory Buffer Size: 32
• Operating Supply Voltage (typ): 3.3V
• Fiber Support: Yes
• Integrated Led Drivers: Yes
• Phy/transceiver Interface: MII
• Power Supply Type: Analog/Digital
• Data Rate (typ): 10/100Mbps
• Vlan Support: Yes
• Operating Temperature (max): 85C
• Operating Temperature (min): -40C
• Mounting: Surface Mount
• Jtag Support: No
• Operating Supply Voltage (max): 3.5V
• Operating Supply Voltage (min): 3.1V
• Operating Temperature Classification: Industrial
• Data Rate: 100Mbps
• Lead Free Status / RoHS Status: Supplier Unconfirmed

Micrel, Inc.
MAC Operation
The KSZ8842-PMQL/PMBL strictly abides by IEEE 802.3 standards to maximize compatibility. Additionally, there is an
added MAC filtering function to filter unicast packets. The MAC filtering function is useful in applications such as VoIP
where restricting certain packets reduces congestion and thus improves performance.
Inter Packet Gap (IPG)
If a frame is successfully transmitted, the minimum 96-bits time for IPG is measured between two consecutive packets.
If the current packet is experiencing collisions, the minimum 96-bits time for IPG is measured from Carrier Sense (CSR)
to the next transmit packet.
Back-Off Algorithm
The KSZ8842-PMQL/PMBL implements the IEEE standard 802.3 binary exponential back-off algorithm in half-duplex
mode, and optional "aggressive mode" back-off. After 16 collisions, the packet is optionally dropped depending on the
switch configuration in SGCR1[8].
Late Collision
If a transmit packet experiences collisions after 512 bit times of the transmission, the packet is dropped.
Illegal Packet Size
The KSZ8842-PMQL/PMBL discards packets that are less than 64 bytes in size and can be programmed to accept
packet sizes up to 1536 bytes in SGCR2[1]. The KSZ8842-PMQL/PMBL can also be programmed for special
applications to accept packet sizes up to 1916 bytes in SGCR2[2].
Flow Control
The KSZ8842-PMQL/PMBL supports standard 802.3x flow control frames on both transmit and receive sides.
On the receive side, if the KSZ8842-PMQL/PMBL receives a pause control frame, the KSZ8842-PMQL/PMBL will not
transmit the next normal frame until the timer, specified in the pause control frame, expires. If another pause frame is
received before the current timer expires, the timer will be updated with the new value in the second pause frame.
During this period (while it is flow controlled), only flow control packets from the KSZ8842-PMQL/PMBL are transmitted.
On the transmit side, the KSZ8842-PMQL/PMBL has intelligent and efficient ways to determine when to invoke flow
control. The flow control is based on availability of the system resources, including available buffers, available transmit
queues, and available receive queues.
The KSZ8842-PMQL/PMBL will flow control a port that has just received a packet if the destination port resource is
busy. The KSZ8842-PMQL/PMBL issues a flow control frame (XON), containing the maximum pause time defined in
IEEE standard 802.3x. Once the resource is freed up, the KSZ8842-PMQL/PMBL sends out the other flow control
frame (XOFF) 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 (not in IEEE 802.3 standards) is also provided. The activation and deactivation
conditions are the same in full-duplex mode. If backpressure is required, the KSZ8842-PMQL/PMBL 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 KSZ8842-
PMQL/PMBL 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 switch 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 collisions and carrier sense is
maintained to prevent packet reception.
To ensure no packet loss in 10 BASE-T or 100 BASE-TX half-duplex modes, the user must enable the following:
Note: These bits are not set by default, since this is not the IEEE standard.
October 2007
1. Aggressive back off (bit 8 in SGCR1)
2. No excessive collision drop (bit 3 in SGCR2)
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KSZ8842-PMQL/PMBL
M9999-100207-1.5