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Altera_Forum's avatar
Altera_Forum
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19 years ago

Tristating LVDS in Cyclone

In my design there is a Cyclone with LVDS transmitter that is always powered (in standby)

The LVDS interface is connected to an LVDS receiver in a STRATIXII device that is not always powered.

If the LVDS transmitter is powered it will always send a differential '0' or a '1'. I.e. there will always be a voltage on the line (+/-1.4V on LVDS_p referred to GND and +/- 1V on LVDS_n referred to GND).

Now, if the STRATIXII device is not powered, it will have 1.4V on the LVDS_p line of the receiver. This is not a healthy situtation. Ideally, the LVDS I/Os should be tristated.

Is there a solution to this problem?

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    19 years ago

    Tristating LVDS is not possible.

    But : In my case it is not necessary because the Stratix II ( and cycloneII too) has the hot socket feature.

    See - http://www.altera.com/literature/hb/stx2/stx2_sii51004.pdf

    ■ The device can be driven before power-up without any damage to the device itself.

    So, leaving LVDS powered, while the Stratix is not powered is no issue.:D
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    19 years ago

    I too have not been successful in creating tri-state lvds drivers on the cyclone II's.

    I'm not sure its possible unfortunately.