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Cyclone for STMicro: TVCC signal in SWD mode
Grigory E. Aug 7, 2017 at 02:43 PM (14:43 hours)
Staff: Takao Y.

  • Hello

    We're preparing to mass production and decided to use Cyclone for STMicro. However we faced with one issue (actually it's not clear for User Manual).

    Right now we are using ST-LINK and SWD mode for uploading a firmware to our device. ST-LINK allows to use only three signal in SWD mode: SWCLK, SWDIO and GND (it's possible not to use TVCC). According to Cyclone for STMicro User Manual we should connect TVCC signal too. The question is whether it's possible to work without TVCC or this signal is required for correct work? I guess Cyclone for STMicro has input buffer and TVCC signal is required for correct work, but I'm not absolutely sure about this.

    Thanks in advance


  • Greetings,

    The TVCC is necessary to power up the internal buffers to determine the reference voltage of the device. Our hardware interface cannot assume that 3V is a high signal. It could be a floating signal for a 5V part.

    Typically the TVCC comes from the chip itself, however, there are workarounds where you can use an external 3V signal (or 5V if your chip is running off 5V) connected to TVCC so that you do not need to change your schematic.

    Takao Yamada

    • Hi

      Thank you for you help. We will try to use workaround you described.

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