I am using Dual Motor Development Kit TMDS2MTRPFCKIT and, until a few minutes ago, I had a problem running my program from Flash without the emulator (in stand-alone mode). Turns out that because of the USB isolation circuit (used to communicate with the pc) on the development kit, powering up the board with or without the USB from the computer plugged into the board defaults with the TRSTn pin being held high (which makes the TMS320F28035 DSP believe the JTAG is in control, eventhough no JTAG is connected). This condition is caused by the default output High state of the USB isolator IC ISO7240C when the input is floating or unpowered. The non-isoloated side of the isolator receives power from the non-isolated side when I power up the board, which outputs the High state on the TRSTn signal. When I plug in the USB connector then remove it from the board, the USB powers up the isolated side long enough to drive the TRSTn-ISO / TRSTn signal low so that it releases JTAG control and allows my program to run from Flash in stand-alone mode. What I'm wondering is if anyone else has observed this same behavior and / or is there a tech note on this somewhere that I just missed? This issue took me a couple days to figure out after verifying that my other stuff was configured properly (boot mode pins, configuration files, etc.). Hope this helps anyone else that might be scratching their head.......I wonder if this issue also exists on other development kits?
I have a similar development board (TMDSHVMTRPFCKIT) that has an isolated XDS100v1 - I don't recall seeing this behaviour, but it may have been by chance.
Interesting note regarding the TRST line... although this line should have a pull-down (check here), per your description it seems the ISO part itself should have a pull down as well...
In this case I will move this thread to the device forum as well, since the development board experts may have additional comments.
According to the ISO7240C datasheet, it won't matter if there is a pulldown resistor on the input side (isolated side) of the isolator when the input side is unpowered. The output will default to the High state in this condition. Only when the input side is powered (through the USB cable) will a low state drive the output Low. That is why I had to momentarily connect the USB cable then remove it to drive a low signal at the input (isolated) side so that it would drive the TRSTn signal low and release the JTAG for my software to run in stand-alone mode.
Jim,Note that on the F28035 controlCARD (R1.2 and up) there is a switch that can be used to connect/disconnect the TRSTn to the MCU.Thank you,Brett
Thanks Brett. Unfortunately, I have a Rev 1.1 control card that doesn't have the TRSTn switch. I purchased the kit last December, so either I got a kit that's been sitting around for awhile or Rev 1.2 got released after December. Either way, it's good that TI has a workaround for the later rev boards and I'm glad that I'm aware of the issue and resolved the problem. I wanted to make others aware of the issue to help with their troubleshooting efforts.
Jim,Too bad, but I'm glad you've now gotten the system to work. Thanks for posting your resolution too, this kind of thing does help others!Regards,Brett
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