SWD connections to LPC1768

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    Paul Curtis

    The SWD adapter supports both JTAG and SWD mode without any changes to the Cortex connector.  I have no idea how to connect from an SWD connector to the pins on an LPC1768, we just take it to the Cortex connector.  If you wish to use the pin connected to TDI as a GPIO in SWD mode, you need to pull off the jumper on the SWD adapter board.

    I suggest you take a look at a Keil MCB1768 schematic to see how they wired up the Cortex connector...

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    Matt

    Thanks Paul, I should (as usual) have been more clear.

    There are many designs out there trying to keep JTAG on the same connector as SWD so that, with another interface cable, you can preserve use of tools people may have.  I was trying to do the same here.  The Keil schematic has a dedicated SWD connector and a dedicated JTAG connector.  Most signals are common, but RTCK and TRST are not.  However, the SWD connector brings out TDI as well,which isn't part of the SWD signal requirements.

    So it seems that you could make an interface that uses the smaller SWD connector on a board, but then wires out to a standard JTAG adapter (like the CrossConnect) if a user didn't have SWD yet. But RTCK and !TRST are not on the SWD connector, so I was trying to squeeze one on the remaining SWD pin.

     

    Anyway, let me ask a more direct question.  On your SWD adapater for CrossConnect, is there any physical use / connection to pin 7?  If our design had a signal on that pin, would that screw up your SWD adapter?

     

    Thanks Paul!

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    Paul Curtis

    The 10-pin Cortex connector supports both JTAG and SWD.  And so does the 20-pin connector, it supports both SWD and JTAG.  There is no "dedicated" anything.  The 10-pin Cortex connector ("SWD connector" in your speak) certainly does bring out TDI even though SWD doesn't need it, that's used when you want to run JTAG over the 10-pin Cortex connector.

    Pin 7 on the Cortex connector is for RTCK which is a requirement on the Cortex connector.

    I suggest you take a look at the connection here for the pinout of the Cortex connector in ARM mode (JTAG) and SWD mode:

    http://www.keil.com/support/man/docs/ulink2/ulink2_hw_connectors.htm

    When in SWD mode, the signal is still routed through the connector, it's not a N/C.  But no, it would not screw up the adapter.

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    Matt

    Thanks Paul, that clears it up.  The MCB board schematic actually leaves RTCK disconnected and labels it "KEY", so it seemed a bit of a disconnect.  However, they obviously aren't using the SWD as JTAG since they have a dedicated JTAG i guess.  Thanks again,

    Matt

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