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KSZ8765CLXCC View Datasheet(PDF) - Micrel

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KSZ8765CLXCC Datasheet PDF : 153 Pages
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Micrel, Inc.
KSZ8765CLX
Functional Overview: Media Access Controller (MAC)
Media Access Controller Operation
The KSZ8765CLX strictly abides by IEEE 802.3 standards to maximize compatibility.
Inter-Packet Gap (IPG)
If a frame is successfully transmitted, the 96-bit time IPG is measured between the two consecutive MTXEN. If the current
packet is experiencing collision, the 96-bit time IPG is measured from MCRS and the next MTXEN.
Backoff Algorithm
The KSZ8765CLX implements the IEEE 802.3 standard binary exponential backoff algorithm and optional “aggressive
mode” backoff. After 16 collisions, the packet will optionally be dropped depending upon the chip configuration in Register
3.
Late Collision
If a transmit packet experiences collisions after 512-bit times of the transmission, the packet will be dropped.
Illegal Frames
The KSZ8765CLX discards frames less than 64 bytes and can be programmed to accept frames up to 1536 bytes in
Register 4. For special applications, the KSZ8765CLX can also be programmed to accept frames up to 2k bytes in
Register 3 bit [6]. Because the KSZ8765CLX supports VLAN tags, the maximum sizing is adjusted when these tags are
present.
Flow Control
The KSZ8765CLX supports standard IEEE 802.3x flow control frames on both transmit and receive sides.
On the receive side, if the KSZ8765CLX receives a pause control frame, the KSZ8765CLX 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 KSZ8765CLX will be transmitted.
On the transmit side, the KSZ8765CLX 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 KSZ8765CLX flow controls a port that has just received a packet if the destination port resource is busy. The
KSZ8765CLX issues a flow control frame (XOFF) containing the maximum pause time defined in the IEEE 802.3x
standard. Once the resource is freed up, the KSZ8765CLX 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 KSZ8765CLX flow controls all ports if the receive queue becomes full.
July 23, 2014
26
Revision 1.0
 

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