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I have an FS SFP (SFP-GB-GE-T 1000BASE-T SFP 100m).

My device has some I/O pins such as TX_DISABLE, RATE_SELECT_1 and RATE_SELECT_0, etc. I am having a hard time finding documentation on these physical pins (not the EEPROM registers, rather the physical pins).

My question is, when the SFP device first turns on do I need to toggle the TX_DISABLE (LOW is on, HIGH is off) before first using it? Or is there some type of wake up procedure that I need to follow? Also, how long should I keep the TX_DISABLE for before enabling it?

Next, if I want to reboot my device, should I set TX_DISABLE to HIGH (turning it off) before power cycling?

Any resources detailing the pin interface would be very helpful.

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  • \$\begingroup\$ this sounds like you "your device" isn't meant to drive an SFP transceiver directly! "Rate select" is not something that a SFP does – it's basically just a relatively dumb converter between differential signal at the TXD pins to whatever the medium (single or multimode fiber, twisted pair, twinax…) does, and vice versa. \$\endgroup\$ May 17, 2022 at 19:45
  • \$\begingroup\$ @MarcusMüller, thank you for your reply. This SFP module is wired up to an FPGA on a development board. We have a copper SFP plugged in and are normally able to ping it and send/receive UDP packets. It sounds like we don't need to worry too much about the rate select pins. We just keep them HI, but it sounds like they aren't too important. Do you have any insight on how we should be using the tx_disable pins? Thanks again. \$\endgroup\$
    – CakeMaster
    May 17, 2022 at 19:55
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    \$\begingroup\$ The rate select pins are optional, and more or less up to the vendor what function they want them to control. Typically they're for putting a module into a lower rate mode (for example to enable a 10 Gbps module to operate at 1 or 2.5 Gbps). \$\endgroup\$
    – The Photon
    May 17, 2022 at 20:36

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My question is, when the SFP device first turns on do I need to toggle the TX_DISABLE (LOW is on, HIGH is off) before first using it?

Not for any SFP module I'm familiar with. Some require an I2C message to a particular register (A2h reg 118) before they will enter "high power mode" and enable their lasers.

Any resources detailing the pin interface would be very helpful.

The relevant specifications are freely available here. SFF-8419 is probably the most important for answering your questions.

See SFF-8472 for details on the software controllable power and rate select registers.

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