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Finisar's 1000BASE-T SFP transceivers (FCLF-8521-3) are based on the SFP Multi Source Agreement (MSA). They are compatible with Gigabit Ethernet and 1000BASE-T standards as specified in IEEE Std. 802.3:2002.
The FCLF-8521-3 versions are fully RoHS compliant. This Application Note covers the most commonly asked questions about Finisar's 1000BASE-T SFPs.
Q: What cable type is suggested for use with the FCLF-8521-3?
A: The FCLF-8521-3 was designed to operate using standard Cat 5 cable that has been configured per IEEE802.3:2002. You can safely use Cat 5e or Cat 6 cables, as these are improved versions of Cat 5. For short cable runs, with intricate routing, stranded cable is recommended, as it is more flexible.
Q: How do you configure the module for 10/100/1000BASE-T operation including RxLOS functionality at all three data rates?
A: The FCLF-8521-3 can be used with a SGMII rev. 1.5 interface (without clocks). This interface supports 10, 100 and 1000BASE-T modes of operation, as mentioned above. The figure below shows how to enable SGMII and advertise all speeds and full/half-duplex using register writes to the PHY over the 2-wire serial interface. A simple power cycle will return the module to default operation.
Q: What is the difference between the FCLF-8521-3 and the FCxx-8520-3?
The FCLF-8521-3 is designed to be a 1000BASE-X compliant device that functions properly in any slot designed for optical SFP's, with no hardware or software changes to the host system. The PHY is configured to perform 1000BASE-X auto-negotiation with the host system. The FCLF-8521-3 does not have link detection circuitry - the RxLOS pin is internally grounded.
The FCLF-8520-3 is similar to the FCLF-8521-3, but the 1000BASE-X auto-negotiation is disabled.
Q: Does the FCLF-8521-3 support 1000BASE-X auto-negotiation from the host system?
A: The 1000BASE-X auto-negotiation from the host systems is supported and must be enabled when using the FCLF-8521-3.
Q: When using the FCLF-8521-3, does the host know that it is driving a copper transceiver?
A: No, to the host system, Finisar's FCLF-8521-3 will appear to be a fiber transceiver. From the host's perspective, acknowledgements received during the 1000BASE-X auto-negotiation process are coming from the remote link partner even though they are coming from the FCLF-8521-3.
Q: When using the FCLF-8521-3, what keeps the 1000BASE-X auto-negotiation from finishing before the 1000BASE-T auto-negotiation?
A: The FCLF-8521-3 will hold back acknowledgement to the host until the copper auto-negotiation (1000BASE-T AN) is resolved, and then it will send the 1000BASE-X auto-negotiation advertisements and acknowledgement information. This way, the host can complete 1000BASE-X auto-negotiation without knowing copper auto-negotiation was involved. This process will slow down 1000BASE-X auto-negotiation, because it will be delayed until the 1000BASE-T auto-negotiation is complete (<3 seconds).
Q: How are abilities resolved between the host and the FCLF-8521-3 during auto-negotiation?
A: The module PHY is able to incorporate the host system's abilities in the cable-side auto-negotiation. Particularly, the module PHY first receives the abilities from the host system during 1000BASE-X auto-negotiation, but the 1000BASE-X auto-negotiation is not yet permitted to complete and no abilities are passed to the host system. The PHY then incorporates the host system's abilities into the 1000BASE-T auto-negotiation. Finally, the result of the 1000BASE-T auto-negotiation is passed on to the host system and the 1000BASE-X auto-negotiation is permitted to complete. The resolution of the 1000BASE-T auto-negotiation will therefore be compatible with the resolution of the 1000BASE-X auto-negotiation.
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