KS8995X Micrel Inc, KS8995X Datasheet - Page 22

• Manufacturer Part Number: KS8995X
• Description: Special Function IC
• Manufacturer: Micrel Inc

Specifications of KS8995X

• Leaded Process Compatible: No
• Peak Reflow Compatible (260 C): No
• Applications: *
• Mounting Type: Surface Mount
• Package / Case: 128-MQFP, 128-PQFP
• Number Of Primary Switch Ports: 5
• Internal Memory Buffer Size: 64
• Operating Supply Voltage (typ): 1.8/2.5/3.3V
• Fiber Support: Yes
• Integrated Led Drivers: Yes
• Phy/transceiver Interface: MII/SNI
• Power Supply Type: Analog/Digital
• Package Type: PQFP
• Data Rate (typ): 10/100Mbps
• Vlan Support: Yes
• Operating Temperature (max): 70C
• Operating Temperature (min): 0C
• Pin Count: 128
• Mounting: Surface Mount
• Jtag Support: No
• Operating Temperature Classification: Commercial
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With: 576-1021 - BOARD EVAL EXPERIMENT KS8995X
• Lead Free Status / RoHS Status: Not Compliant, Contains lead / RoHS non-compliant

KS8995X
MAC (Media Access Controller) Operation
The KS8995X 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 KS8995X implements the IEEE Std 802.3 binary exponential back-off algorithm, and optional “aggressive mode” back off.
After 16 collisions, the packet will be optionally dropped depending on the chip configuration in Register 3. See “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 KS8995X discards frames less than 64 bytes and can be programmed to accept frames up to 1536 bytes in Register 4.
For special applications, the KS8995X can also be programmed to accept frames up to 1916 bytes in Register 4. Since the
KS8995X supports VLAN tags, the maximum sizing is adjusted when these tags are present.
Flow Control
The KS8995X supports standard 802.3x flow control frames on both transmit and receive sides.
On the receive side, if the KS8995X receives a pause control frame, the KS8995X 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 KS8995X will be transmitted.
On the transmit side, the KS8995X 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 KS8995X will flow control a port, which just received a packet, if the destination port resource is being used up. The
KS8995X will issue a flow control frame (XOFF), containing the maximum pause time defined in IEEE standard 802.3x. Once
the resource is freed up, the KS8995X will send 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 provided to prevent the flow control mechanism from being
activated and deactivated too many times.
The KS8995X will flow control all ports if the receive queue becomes full.
Half-Duplex Back Pressure
A half-duplex back pressure option (note: not in 802.3 standards) is also provided. The activation and deactivation conditions
are the same as the above in full-duplex mode. If back pressure is required, the KS8995X will send preambles to defer the other
stations’ transmission (carrier sense deference). To avoid jabber and excessive deference defined in 802.3 standard, after a
certain time it will discontinue the carrier sense but it will raise the carrier sense quickly. This short silent time (no carrier sense)
is to prevent other stations from sending out packets and keeps other stations in carrier sense deferred state. If the port has
packets to send during a back pressure situation, the carrier-sense-type back pressure will be interrupted and those packets
will be transmitted instead. If there are no more packets to send, carrier-sense-type back pressure will be active again until
switch resources are free. If a collision occurs, the binary exponential backoff algorithm is skipped and carrier sense is
generated immediately, reducing the chance of further colliding and maintaining carrier sense to prevent reception of packets.
To ensure no packet loss in 10BaseT or 100BaseTX half-duplex modes, the user must enable the following:
These bits are not set as the default because this is not the IEEE standard.
M9999-120403
• Aggressive backoff (register 3, bit 0)
• No excessive collision drop (register 4, bit 3)
• Back pressure (register 4, bit 5)
22
December 2003
Micrel