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AM79C988A 数据表(PDF) 8 Page - Advanced Micro Devices |
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AM79C988A 数据表(HTML) 8 Page - Advanced Micro Devices |
8 / 25 page 8 Am79C988A PRELIMINARY FUNCTIONAL DESCRIPTION Overview The Am79C988A Quad Integrated Ethernet Transceiver (QuIET™) device consists of four independent 10BASE-T transceivers which are compliant with the IEEE 802.3 Sec- tion 14 ( Medium Attachment Unit for 10BASE-T Cabling) standard. The QuIET device includes on-chip filtering for both transmit and receive functions, thus eliminating the need for external filters. It provides automatic polarity detection and correction and can operate in either normal or full-duplex mode. The QuIET device interfaces directly with the Pseudo AUI (PAUI™) ports on the IMR2 (Am79C983A) device. PAUI ports are functionally equivalent to the AUI inter- face as described in IEEE 802.3 Section 7, but are single-ended and do not have the drive capability specified in the standard. The QuIET device can also be connected to standard AUI ports. Command and status data is exchanged with the IMR2 device via a serial management interface. Twisted Pair Transmitters Each TXD port is a differential twisted pair driver. When properly terminated, TXD meets the 10BASE-T trans- mitter electrical requirements as specified in IEEE 802.3 Section 14.3.1.2. Proper termination, Figure 1, consists of a single 110 ohm +1% resistor across TXD+ and TXD- and a 1:1 standard Ethernet transformer. A common mode may be required for EMI considerations. An ex- ternal capacitor is not required. The load is a twisted pair cable that meets IEEE 802.3, Section 14.4 require- ments. The cable is terminated at the other end by a 100 ohm load. The TXD signal is filtered on the chip to reduce harmonic content per IEEE 802.3 Section 14.3.2.1 (10BASE-T). Since filtering is performed by the QuIET device, the TXD signal can be connected directly to a standard transformer. External filter modules are not required. Figure 1. TXD Termination Twisted Pair Receivers Each RXD port is a differential twisted-pair receiver. When properly terminated, RXD ports will meet the elec- trical requirements for 10BASE-T receivers as specified in IEEE 802.3, Section 14.3.1.3. Proper termination is shown in Figure 2. Each receiver has internal filtering and does not require external filter modules. Figure 2. RXD Termination Receive squelch threshold voltage can be programmed for extended distance mode. In this mode, the differential receive threshold is reduced to allow cable lengths greater than the 100 meters specified in the IEEE 802.3 Standard. Polarity Detection and Reversal The receive function includes the ability to invert the po- larity of the signals appearing at the RXD+ pair if the polarity of the received signal is reversed (such as in the case of a wiring error). The polarity detection function is activated following Reset or Link Fail, and will reverse the receive polarity based on both the polarity of any previous Link Test Pulses and the polarity of subsequent packets with a valid End Transmit Delimiter (ETD). When in the Link Fail State, the QuIET device will recog- nize Link Test Pulses of either positive or negative polar- ity. Exit from the Link Fail state is caused by the reception of five-to-seven consecutive Link Test Pulses of identical polarity. Both Link Test Pulses and packets are used to determine the initial receive polarity. Once correct polarity is established, the receiver subsequently accepts only Link Test Pulses that are recognized as TRUE rather than inverted. The Link Test pulse follows the template of Figure 14-12 of the IEEE 802.3 10BASE-T standard. Link Test Function The Link Test function is implemented as specified in the IEEE 802.3 10BASE-T standard. A Link Test pulse is transmitted if a port has been idle for a period of more than approximately 16 (+/-8) milliseconds (ms). The QuIET device monitors the 10BASE-T ports for packet and Link Pulse activity. If neither a packet nor a Link Test pulse is received for 79 ms to 102 ms, the port will enter the Link Test Fail State and the QuIET device will inhibit the transmit and receive functions for that port. Link pulses are transmitted when idle conditions are met. When a packet or five-to-seven consecutive Link Test pulses is received, the port exits the Link Fail State and transmit/receive functions are restored. 19880B-5 TXD+ TXD- 110 Ω 1:1 Twisted Pair 100 Ω RXD+ RXD- 1:1 Twisted Pair 100 Ω 100 Ω 19880B-6 |
类似零件编号 - AM79C988A |
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类似说明 - AM79C988A |
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