KSZ8895MQ_12 MICREL [Micrel Semiconductor], KSZ8895MQ_12 Datasheet - Page 32

• Manufacturer Part Number: KSZ8895MQ_12
• Description: Integrated 5-Port 10/100 Managed Ethernet Switch with MII/RMII interface
• Manufacturer: MICREL [Micrel Semiconductor]

Micrel, Inc.
KSZ8895MQ/RQ/FMQ
Flow Control
The KSZ8895MQ/RQ/FMQ supports standard 802.3x flow control frames on both transmit and receive sides.
On the receive side, if the KSZ8895MQ/RQ/FMQ receives a pause control frame, the KSZ8895MQ/RQ/FMQ 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 (being flow controlled), only flow control packets from the KSZ8895MQ/RQ/FMQ will be
transmitted.
On the transmit side, the KSZ8895MQ/RQ/FMQ 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 KSZ8895MQ/RQ/FMQ flow controls a port that has just received a packet if the destination port resource is
busy. The KSZ8895MQ/RQ/FMQ issues a flow control frame (XOFF), containing the maximum pause time defined in
IEEE standard 802.3x. Once the resource is freed up, the KSZ8895MQ/RQ/FMQ sends out the other flow control
frame (XON) with zero pause time to turn off the flow control (turn on transmission to the port). A hysteresis feature is
also provided to prevent over-activation and deactivation of the flow control mechanism.
The KSZ8895MQ/RQ/FMQ flow controls all ports if the receive queue becomes full.
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March 2012
M9999-032612-1.5