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LAN8820I Datasheet(PDF) 15 Page - Microchip Technology |
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LAN8820I Datasheet(HTML) 15 Page - Microchip Technology |
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15 / 83 page  2009-2015 Microchip Technology Inc. DS00001871B-page 15 LAN8820/LAN8820I 3.1.5 MANUAL OPERATION The device supports a manual (forced) operation for test purposes. In manual operation, the user sets the link speed (10Mbps or 100Mbps) and the duplex state (full or half). Auto-negotiation must be disabled in order to manually configure the speed and the duplex. This may be accomplished using the configuration pins, as described in Section 3.8.1.2.2, "Configuring the Mode of Operation (CONFIG[3:2])," on page 26, or by using the Basic Control Register register as described in Section 3.1.2, "Disabling Auto-negotiation," on page 14. For 10BASE-T and 100BASE-TX, the link state of the device is determined by the Speed Select[1], Speed Select[0], and Duplex Mode bits of the Basic Control Register. Manual operation at a link speed of 1000Mbps is not supported. 3.1.6 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 internal carrier sense signal, CRS, responds to both transmit and receive activity. 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 and collision detection is disabled. In this mode, the internal CRS responds only to receive activity. In 10BASE-T and 100BASE-T mode, CRS is redefined to respond only to received activity. In 1000BASE-T, CRS is disabled. Table 3-2 describes the behavior of the internal CRS bit under all receive/transmit conditions. Manual Master Multi-Port Master Slave Manual Master Manual Master No Link No Link Manual Master Manual Slave Master Slave Manual Slave Single-Port Slave Master Manual Slave Multi-Port Slave Master Manual Slave Manual Master Slave Master Manual Slave Manual Slave No Link No Link TABLE 3-2: CRS BEHAVIOR Mode Speed Duplex Activity CRS Behavior ( Note 3-1) 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 TABLE 3-1: MASTER/SLAVE RESOLUTION FOR 1000BASE-T (CONTINUED) |
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