TNETX3150 datasheet(28/113 Pages) TI1

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TNETX3150/TNETX3150A

ThunderSWITCH™ 15-PORT 10-/100-MBIT/S ETHERNET™ SWITCH

SPWS027F – FEBRUARY 1997 – REVISED SEPTEMBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

uplink-flow control protocol

The 200-Mbit/s handshake protocol is as follows:

D The upstream device holds flow-control signal (M00COL) high, preventing the TNETX3150/TNETX3150A

from transmitting frames on the uplink.

D When a frame is ready to transmit, the TNETX3150/TNETX3150A makes a request to the upstream device

by taking M00TXD00 high.

D When ready to receive, the upstream device, in response to seeing M00TXD00 go high, takes M00COL

low.

D The TNETX3150/TNETX3150A places the source port number on bits M00TXD00–M00TXD03.

D Four M00TCLK clock cycles after M00COL is driven low, M00TXEN is taken high and normal data transfer

occurs, starting with the destination address. No preamble is provided before the destination address in the

frame.

D When M00TXEN is taken low at the end of the frame, M00COL is taken high in preparation for the next

handshake. If the upstream device is busy, M00COL should be kept high even after M00TXD00 is taken

high, until the upstream congestion has cleared and transmission can continue. The next frame

transmission does not proceed until the handshake is performed. M00COL must be cycled before each

transmission.

D To operate in this mode M00UPLINK is held low, M00DUPLEX and M00PROTOCOL are held high, and the

in-order broadcast (IOB) option bit in the SYSCTRL register is set.

uplink frame control

If the uplink transmit FIFO underruns, a frame control-signal is provided on M00TXER during 200-Mbit/s uplink

operation to permit the reconstruction of frames using external logic (see Figure 10).

In uplink mode, M00TXER is low throughout a successful transmission. If a FIFO underrun occurs (due to

exceeding maximum memory bandwidth), the data in the FIFO continues to be transmitted until empty, at which

point the M00TXER signal is taken high. While M00TXER is high, the data transmitted from the uplink should

be discarded. When the next 64-byte data buffer is forwarded to the uplink transmit port, M00TXER is taken

low and normal transmission continues. If the following buffer updates are delayed, the FIFO again underruns,

causing M00TXER to go high once the data present in the FIFO is transmitted.

M00TXCLK

M00TXD7-M00TXD0

M00TXEN

Don’t Care

Byte 0

Don’t Care

M00TXER

128 bytes

Minimum Transmission

64 bytes

Minimum Transmission

Byte n

Byte n+1

Byte n+i

Byte n+i+1

Byte m

Figure 10. Uplink Frame Control for External Frame Reconstruction

TNETX3150 数据表(PDF) 28 Page - Texas Instruments

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