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MultiLink, MultiLink Universal (FX) Circuit Protection
Bryan D. Apr 20, 2016 at 12:49 PM (12:49 hours)
Staff: Gerardo R.

  • What circuit protection, if any, is provided on the MultiLink programmer JTAG / programming signals?  Is there any transient protection, any series resistance, any isolation, etc.?  If someone wanted to add isolation, would the MultiLink be able to power one side of the isolator while the target board powered the other side?




    Comments

  • There are 47ohm terminating resistors on each header pin. On the VCC and RESET lines we have a 5.6V Zener diode to sink any transient spikes. This setup does not guarantee complete electrical isolation and it's not unheard of that customer boards can damage the Multilink's input buffers. If you are at all concerned about this you should add an electrical isolator. The Multilink will be able to provide 5/3.3V.

  • What is the max data rate on the 6-pin header (i.e. BKGD pin) for the S12 MCUs?  I can find bi-directional isolators (e.g. I2C) but am unsure those would support high enough data rates.

  • Are the 5.6V zener diodes unidirectional or bidirectional?
    Also, assuming the "47ohm terminating resistors" are series termination?

  • -The data rate is equivalent to your target's bus frequency (System clock/2) and the fastest on the S12 MCUs that I've seen was 50Mhz.
    -The zener is unidirectional with the cathode attached to the header pin and the anode connected to ground.
    -The terminating resistors are series resistors.

  • Is the same type of protection provided on the JTAG signals on, for example, the 10-pin and 14-pin headers (i.e. TDO, TDI, TCLK, etc.)?

    What is the maximum current sourcing/sinking capability of the programming signals (BKGD as well as JTAG signals)? Is the 47-ohm series enough to limit current and protect these signals in the event of a short-circuit or is further protection required?

  • The zener diode only exists on the VCC and RESET lines. Terminating resistors exist on all header pins including the JTAG header. Unfortunately, we have not measured the maximum current sourcing/sinking of the programming headers. They are connected to these two ICs so you can infer current ratings from their datasheets SN74LVC2G126DCT LVX4245MTCX.

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