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TNETE2008PBE Datasheet(PDF) 10 Page - Texas Instruments |
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TNETE2008PBE Datasheet(HTML) 10 Page - Texas Instruments |
10 / 33 page TNETE2008 OctalPHY EIGHT 10BASE-T PHYSICAL-LAYER INTERFACES SPWS042B – DECEMBER 1997 – REVISED JUNE 1998 10 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 10BASE-T differential line-transmitter function Each TNETE2008 differential line driver drives a balanced, properly terminated twisted-pair transmission line with a nominal characteristic impedance of 100 Ω. In the idle state, the driver maintains a minimum differential output voltage while staying within the required common-mode voltage range. The driver incorporates an on-chip wave-shaping and high-frequency filtering stage so the outputs can be connected directly to isolation transformers through series-termination resistors. No external filters are required. After transmission has ceased on a PHY, and for a minimum of 250 ns, the driver maintains full differential outputs, which thereafter begin to decay to the minimum differential level. Each PHY also transmits regular link pulses in compliance with IEEE Std 802.3. In half-duplex mode, interface carrier sense (IFCRS) asserts during transmits. 10BASE-T differential line-receiver function The line-receiver terminals of each PHY must be connected to a properly terminated transmission line via an external isolation transformer. The receiver establishes its own common-mode input-bias voltage. Data received from the network is output on the IFRXD terminals of the interface. The receiver incorporates an intelligent squelch function that allows incoming data to pass only if the input amplitude is greater than a minimum signal threshold and a specific pulse sequence is received. This protects against impulse line noise being mistaken for signal or line activity. The squelch circuits quickly deactivate if received pulses fall outside the specifications. Over-long pulses are not mistaken as link pulses. There are two choices for signal thresholds via the RCVTHRESH terminal. Selecting the lower squelch value (selected by pulling RCVTHRESH high) may operate over longer cables but does not meet IEEE minimum squelch levels. For this reason, it is recommended that this terminal be tied low. Each channel’s squelch circuit contains an MLT-3 (100BASE-T data format) detector, which, when enabled via MLT3BLOCK pulled high, prevents the receiver from opening the squelch when MLT-3 data is present. IFCRS is asserted while the squelch function is active to indicate that the circuit is allowing data to pass from the twisted pair. IFCRS is deasserted when the squelch circuit is disabling data flow, although the receive elastic buffer still may be outputting data. jabber detection Each PHY monitors the length of the packet being transmitted. If a single packet exceeds 24 ms, then a jabber condition is flagged. The output is disabled, the IFCOL (collision) signal is asserted, and the IFCRS signal is deasserted. To clear the jabber function, it is necessary to cease transmission for a minimum of 400 ms. link test When not in autonegotiation mode, each PHY transmits link pulses on the XMTP/XMTN outputs, separated by an interval of 19 ms. The receiver looks for valid link pulses on the input pair. If a link pulse is not received within a given time interval, ≅ 100 ms, then the PHY enters a link-fail state. In this state, link pulses continue to be generated, and the receiver constantly looks for the link-pulse pattern. The PHY remains in this state until a valid receive packet or multiple legal link test pulses are received. When link pulses are not detected, the IFLINK signal is deasserted and transmission of data is inhibited. Also, an activated enabled MLT-3 decoder inhibits the receive function for MLT-3 encoded data and can, therefore, prevent assertion of IFLINK or, if already asserted, cause deassertion of IFLINK if the MLT-3 encoded data persists for longer than 100 ms. |
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