TC9204-DS-R05 datasheet(20/49 Pages) ETC1

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TC9204M

Preliminary Data Sheet

disabled using shared configuration pin DisBPBk or EEPROM. In this case the switch will start

transmitting with minimum IFG after carrier sense is deasserted and followed after collision.

For carrier-based backpressure the switch will use the deferral mechanism rather than the collision

backoff mechanism. The transmit MAC will jam the line by sending continuous preamble. The link

partner will see the channel busy and thus it will defer transmission without imposing any additional

backoff delay. The jamming procedure will have short break to avoid jabber condition and the break will

also be short enough to prevent the other stations from starting transmission. Preamble can be sent this

way as long as necessary. If valid packets became available for transmission during this period then

jamming will be interrupted and the packets will be transmitted with standard IFG (Inter-Frame Gap). In

this case backpressure is executed the same way as collision based mechanism. Carrier based

backpressure can be selected using shared configuration pin CrBP or EEPROM.

Backpressure operation can be disabled globally using the shared configuration pin DisBkPr or per port

basis using the EEPROM. By default forward pressure is also enabled whenever backpressure is

enabled. Forward pressure is executed only in extreme congestion conditions that normally do not occur

often. This flow control procedure is highly efficient in minimizing the packet loss. If desired, the forward

pressure can be disabled by the EEPROM setting.

If a HUB is connected to many workstations, one of the ports may be partitioned in heavy traffic when the

switch executes backpressure. TC9204M can prevent this by discontinuing the backpressure process after

a predefined number of consecutive collisions have reached. This function can be enabled using the

shared configuration pin FullBP or adjusting EEPROM setting. Unlike other settings, to enable this feature

the pin/bit should be set to '0'. The respective number of collisions defaults to 28 and can be specified using

the EEPROM. In addition, when this feature is enabled the MAC will either grant receiving the next packet

without colliding it, after which, it will resume the backpressure, or will completely quit backpressure waiting

for a new XOFF command from internal flow control management device.

Confidential.

20/49

July 29, 2003

TC9204M-DS-R05

TC9204-DS-R05 数据表(PDF) 20 Page - List of Unclassifed Manufacturers