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LAN9115 Datasheet(PDF) 57 Page - Microchip Technology |
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LAN9115 Datasheet(HTML) 57 Page - Microchip Technology |
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57 / 114 page  2005-2016 Microchip Technology Inc. DS00002269A-page 57 LAN9115 4.7.1 RE-STARTING AUTO-NEGOTIATION Auto-negotiation can be re-started at any time by setting register 0, bit 9. Auto-negotiation will also re-start if the link is broken at any time. A broken link is caused by signal loss. This may occur because of a cable break, or because of an interruption in the signal transmitted by the Link Partner. Auto-negotiation resumes in an attempt to determine the new link configuration. If the management entity re-starts Auto-negotiation by writing to bit 9 of the control register, the LAN9115 will respond by stopping all transmission/receiving operations. Once the break_link_timer is done, in the Auto-negotiation state- machine (approximately 1200ms) the auto-negotiation will re-start. The Link Partner will have also dropped the link due to lack of a received signal, so it too will resume auto-negotiation. 4.7.2 DISABLING AUTO-NEGOTIATION Auto-negotiation can be disabled by setting register 0, bit 12 to zero. The device will then force its speed of operation to reflect the information in register 0, bit 13 (speed) and register 0, bit 8 (duplex). The speed and duplex bits in register 0 should be ignored when auto-negotiation is enabled. 4.7.3 HALF VS. FULL-DUPLEX Half-duplex operation relies on the CSMA/CD (Carrier Sense Multiple Access / Collision Detect) protocol to handle net- work traffic and collisions. In this mode, the carrier sense signal, CRS, responds to both transmit and receive activity. In this mode, If data is received while the PHY is transmitting, a collision results. In full-duplex mode, the PHY is able to transmit and receive data simultaneously. In this mode, CRS responds only to receive activity. The CSMA/CD protocol does not apply and collision detection is disabled. Table 4-2 describes the behavior of the CRS bit under all receive/transmit conditions. Note 4-1 The LAN9115 10/100 PHY CRS signal operates in two modes: Active and Low. When in Active mode, CRS will transition high and low upon line activity, where a high value indicates a carrier has been detected. In Low mode, CRS stays low and does not indicate carrier detection. The CRS signal cannot be used as a verification method of transmitted packets when transmitting in 10 or 100 Mbps in full-duplex mode. TABLE 4-2: CRS BEHAVIOR Mode Speed Duplex Activity CRS Behavior (Note 4-1) Manual 10 Mbps Half-Duplex Transmitting Active Manual 10 Mbps Half-Duplex Receiving Active Manual 10 Mbps Full-Duplex Transmitting Low Manual 10 Mbps Full-Duplex Receiving Active Manual 100 Mbps Half-Duplex Transmitting Active Manual 100 Mbps Half-Duplex Receiving Active Manual 100 Mbps Full-Duplex Transmitting Low Manual 100 Mbps Full-Duplex Receiving Active Auto-Negotiation 10 Mbps Half-Duplex Transmitting Active Auto-Negotiation 10 Mbps Half-Duplex Receiving Active Auto-Negotiation 10 Mbps Full-Duplex Transmitting Low Auto-Negotiation 10 Mbps Full-Duplex Receiving Active Auto-Negotiation 100 Mbps Half-Duplex Transmitting Active Auto-Negotiation 100 Mbps Half-Duplex Receiving Active Auto-Negotiation 100 Mbps Full-Duplex Transmitting Low Auto-Negotiation 100 Mbps Full-Duplex Receiving Active |
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