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TMS320F280021: Questions about 20-Pin JTAG Connection

Chanhee Lee
Prodigy 50 points
Part Number: TMS320F280021

Hello,

I had a few questions about Figure 7-18 in the TMS320F28002x datasheet.

The figure shows the 20-pin JTAG header connection, and I had 4 questions:

1) what is open drain and where does it connect to?

2) does the 3.3V supply on pins 13 and 14 come from the MCU? If not, where does it come from?

3) are the GND pins connected to the GND of the MCU? If not, where do I ground them?

4) it says that TDI and TDO connections are optional for cJTAG. I am not sure if I will be using JTAG or cJTAG. Are there any advantages of using cJTAG over JTAG? Would I lose any functionalities if I choose to use cJTAG? 

Thanks in advance!

  • 0
    TI__Mastermind 26481 points
    Chanhee Lee said:
    1) what is open drain and where does it connect to?

    The figure is saying the 20-pin JTAG header provides an open-drain output which can be connected to any reset signals on the target board. For example, you could connect this to the XRSn pin on the MCU.

    Chanhee Lee said:
    2) does the 3.3V supply on pins 13 and 14 come from the MCU? If not, where does it come from?

    The 3.3V supply has to come from the target board.

    Chanhee Lee said:
    3) are the GND pins connected to the GND of the MCU? If not, where do I ground them?

    The GND pins would connect to the GND plane on the target board.

    Chanhee Lee said:
    4) it says that TDI and TDO connections are optional for cJTAG. I am not sure if I will be using JTAG or cJTAG. Are there any advantages of using cJTAG over JTAG? Would I lose any functionalities if I choose to use cJTAG? 

    Speed would be impacted since cJTAG only uses two pins. In general, if you are not pin-limited on your application, I'd recommend sticking with the 4-pin JTAG.