KS8995MA Micrel Inc, KS8995MA Datasheet - Page 26

• Manufacturer Part Number: KS8995MA
• Description: IC SWITCH 10/100 5PORT 128PQFP
• Manufacturer: Micrel Inc

Specifications of KS8995MA

• 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
• Data Rate: 100Mbps
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: 576-1017 - BOARD EVAL EXPERIMENT KS8995M
• Lead Free Status / RoHS Status: Not Compliant, Lead free / RoHS Compliant

KS8995MA
Late Collision
If a transmit packet experiences collisions after 512-bit times of the transmission, the packet is dropped.
Illegal Frames
The KS8995MA discards frames of less than 64 bytes and can be programmed to accept frames up to 1536 bytes in Register
4. For special applications, the KS8995MA can also be programmed to accept frames up to 1916 bytes in Register 4. Since
the KS8995MA supports VLAN tags, the maximum size is adjusted when these tags are present.
Flow Control
The KS8995MA supports standard 802.3x flow control frames on both transmit and receive sides.
On the receive side, if the KS8995MA receives a pause control frame, the KS8995MA 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 given in the second pause frame. During this period of flow control, only flow
controlled packets from the KS8995MA are transmitted.
On the transmit side, the KS8995MA 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 KS8995MA flow controls a port that has just received a packet if the destination port resource is busy. The KS8995MA
issues a flow control frame (XOFF), containing the maximum pause time defined in IEEE standard 802.3x. Once the resource
is freed up, the KS8995MA 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 KS8995MA flow controls all ports if the receive queue becomes full.
Half-Duplex Back Pressure
The KS8995MA also provides a half-duplex back pressure option (note: this is not in IEEE 802.3 standards). The activation
and deactivation conditions are the same as the ones given for full-duplex mode. If back pressure is required, the KS8995MA
sends preambles to defer the other station's transmission (carrier sense deference). To avoid jabber and excessive deference
as defined in IEEE 802.3 standard, after a certain period of time, the KS8995MA discontinues carrier sense but raises it quickly
after it drops packets to inhibit other transmissions. This short silent time (no carrier sense) is to prevent other stations from
sending out packets and keeps other stations in a carrier sense deferred state. If the port has packets to send during a back
pressure situation, the carrier-sense-type back pressure is interrupted and those packets are transmitted instead. If there are
no more packets to send, carrier-sense-type back pressure becomes 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 10BASE-T or 100BASE-TX half-duplex modes, the user must enable the following:
These bits are not set as the default because this is not the IEEE standard.
Broadcast Storm Protection
The KS8995MA has an intelligent option to protect the switch system from receiving too many broadcast packets. Broadcast
packets are normally forwarded to all ports except the source port and thus use too many switch resources (bandwidth and
available space in transmit queues). The KS8995MA has the option to include “multicast packets” for storm control. The
broadcast storm rate parameters are programmed globally and can be enabled or disabled on a per port basis. The rate is based
on a 50ms interval for 100BT and a 500ms interval for 10BT. At the beginning of each interval, the counter is cleared to zero
and the rate limit mechanism starts to count the number of bytes during the interval. The rate definition is described in Registers
6 and 7. The default setting for Registers 6 and 7 is 0x4A (74 decimal). This is equal to a rate of 1%, calculated as follows:
MII Interface Operation
The media independent interface (MII) is specified by the IEEE 802.3 committee and provides a common interface between
physical layer and MAC layer devices. The KS8995MA provides two such interfaces. The MII-P5 interface is used to connect
to the fifth PHY, whereas the MII-SW interface is used to connect to the fifth MAC. Each of these MII interfaces contains two
distinct groups of signals, one for transmission and the other for receiving. Table 1 describes the signals used in the MII-P5
interface.
M9999-051305
• Aggressive backoff (Register 3, bit 0)
• No excessive collision drop (Register 4, bit 3)
• Back pressure (Register 4, bit 5)
148,800 frames/sec ¥ 50ms/interval ¥ 1% = 74 frames/interval (approx.) = 0x4A
26
Micrel, Inc.
May 2005