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I am trying to understand how a micro-controller (in this case a C2000 from TI) communicates with other devices via jtag. The device here is a FT2232 (a jtag to usb converter). According to the figure, would the micro-controller be the "JTAG Controller Connection" and FT2232 the "Device #1"?

I also need to convert the jtag signal to RS-232, and I need to know the directions of jtag. Which channels (TCK, TMS, TDI, TDO) are bi-directional? In other words, does FT2232 (Device #1) ever send a signal to any buses besides TDO?

Typical jtag configuration

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  • \$\begingroup\$ You're going to have to be a lot more specific. What are the "other devices"? What is the purpose of the FT2232? Is there software on the C2000 which manipulates JTAG lines to other things, or is it the JTAG target of something like the FT2232? What is your purpose in converting a JTAG signal to RS232 - eg, what exactly are you trying to accomplish, and why do you think that would help with it? \$\endgroup\$ Dec 12, 2020 at 5:33

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Every JTAG signal is unidirectional. The JTAG controller TCK and TMS pins drives all the JTAG device TCK and TMS pins. (and the TRST pins, if present). Each JTAG device drives only its TDO, not any of the other JTAG lines.

In my admittedly limited JTAG experience, I've only seen the FT2232 used as a JTAG controller, not a JTAG device. The CPU it's connected to is the "JTAG device". a b c

I've never actually used 2-wire SWD ("serial-wire debug"), but I hear it has bidirectional lines and is sometimes is called a "variant of JTAG".

I've seen microcontrollers communicate with a lot of peripherals using daisy-chain SPI, which is very similar to JTAG.

I'm not sure how RS-232 is relevant.

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I have used JTAG where there is a JTAG connector on the board for the controller to plug into. (PC) The JTAG lines go to all the parts. The microcontroller gets programmed through the JTAG bus. Testing is done this way also.

It is possible, to have the onboard micro talk to the other parts through JTAG. Normally I2C or SPI is used to talk to the other parts.

When in JTAG mode, the IC are in reset mode.

The FT2232 has nothing to do with RS232. It is a USB device that can do many different things. I have used it as a JTAG controller. The PC talks to the FT2232 which in turn talks JTAG. From the PC you can place all the parts on the board in reset & JTAG mode. Now the PC can program the micro's memory and set high or low or tristate any pin on the IC on the bus. The state of any pin can be read back to the PC.

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