Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface
Datasheet
7.2.5.1PHY Pause Flow ControlThe Port 1 & 2 PHYs are capable of generating and receiving pause flow control frames per the IEEE 802.3 specification. The PHYs advertised pause flow control abilities are set via bits 10 (Symmetric Pause) and 11 (Asymmetric Pause) of the Port x PHY Auto-Negotiation Advertisement Register (PHY_AN_ADV_x). This allows the PHY to advertise its flow control abilities and auto-negotiate the flow control settings with its link partner. The default values of these bits are determined via configuration straps as defined in Section 14.4.2.5, "Port x PHY Auto-Negotiation Advertisement Register (PHY_AN_ADV_x)," on page 295.
The pause flow control settings may also be manually set via the manual flow control registers Port 1 Manual Flow Control Register (MANUAL_FC_1) and Port 2 Manual Flow Control Register (MANUAL_FC_2). These registers allow the switch fabric ports flow control settings to be manually set when auto-negotiation is disabled or the Manual Flow Control Select bit 0 is set. The currently enabled duplex and flow control settings can also be monitored via these registers. The flow control values in the Port x PHY Auto-Negotiation Advertisement Register (PHY_AN_ADV_x) are not affected by the values of the manual flow control register. Refer to Section 6.2.3, "Flow Control Enable Logic," on page 58 for additional information.
7.2.5.2Parallel DetectionIf the LAN9311/LAN9311i is connected to a device lacking the ability to auto-negotiate (i.e. no FLPs are detected), it is able to determine the speed of the link based on either 100M MLT-3 symbols or 10M Normal Link Pulses. In this case the link is presumed to be half-duplex per the IEEE 802.3 standard. This ability is known as “Parallel Detection.” This feature ensures interoperability with legacy link partners. If a link is formed via parallel detection, then bit 0 in the Port x PHY Auto-Negotiation Expansion Register (PHY_AN_EXP_x) is cleared to indicate that the link partner is not capable of auto- negotiation. If a fault occurs during parallel detection, bit 4 of the Port x PHY Auto-Negotiation Expansion Register (PHY_AN_EXP_x) is set.
The Port x PHY Auto - Negotiation Link Partner Base Page Ability Register (PHY_AN_LP_BASE_ABILITY_x) is used to store the Link Partner Ability information, which is coded in the received FLPs. If the link partner is not auto-negotiation capable, then this register is updated after completion of parallel detection to reflect the speed capability of the link partner.
7.2.5.3Restarting Auto-NegotiationAuto-negotiation can be re-started at any time by setting bit 9 of the Port x PHY Basic Control Register (PHY_BASIC_CONTROL_x). 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 Port x PHY Basic Control Register (PHY_BASIC_CONTROL_x), the LAN9311/LAN9311i will respond by stopping all transmission/receiving operations. Once the internal break link time of approximately 1200ms has passed in the Auto-negotiation state-machine, the auto-negotiation will re-start. In this case, the link partner will have also dropped the link due to lack of a received signal, so it too will resume auto- negotiation.
7.2.5.4Disabling Auto-NegotiationAuto-negotiation can be disabled by clearing bit 12 of the Port x PHY Basic Control Register (PHY_BASIC_CONTROL_x). The PHY will then force its speed of operation to reflect the speed (bit
13)and duplex (bit 8) of the Port x PHY Basic Control Register (PHY_BASIC_CONTROL_x). The speed and duplex bits in the Port x PHY Basic Control Register (PHY_BASIC_CONTROL_x) should be ignored when auto-negotiation is enabled.
