As shown in the figure, the reset circuit uses an ADM706TARZ chip.

In the first two weeks, I found that the DSP could not be connected. Later, I tested both ends of switch S1 and found that the two ends were not connected after the switch was pressed. Later, I changed a switch and the DSP was connected.

Then I can't connect again, what's going on? Each pin of the JTAG interface of the DSP was tested, and each pin was tested after power-on. The voltage value of each pin is posted here as a memo:

TMS——3.05V; TRST——0V; TDI——3.04V; TDO——3.16V; TCK_RET—— 3.03V ; TCK——3.03V; EMU1——3.27V ; EMU2——3.27V; VCC ——3.28V; GND——0V;

The multimeter used in the test was measured in the DC range. Because there was no oscilloscope at hand at that time, I used the multimeter to test it all at once. The DSP JTAG connection is shown in the following figure:

Why can't the TI DSP be connected? The problem that the JTAG interface cannot be connected

Everything works fine, why can't I connect? The switch has been tested several times, and there is no problem a few days ago. The most depressing thing is that sometimes it can be connected, and sometimes it can't be connected. I am a little bit helpless...

In the end, I found that sometimes it can be connected after pressing the reset several times. Is it still a reset problem?

So I tested pin 7 of ADM706TARZ, and found that it is usually low level. After pressing the reset button, it is actually about 1.2V. If it is broken, this chip must be broken...

So I changed to a new one and everything was fine...

Here again I re-emphasize the inspiration I got from this connection to the DSP:

If the DSP cannot be connected all the time, there must be a problem with the hardware connection, please pay special attention to the problem of the reset circuit! ! !

2) The JTAG port of Xilinx FPGA cannot be connected

The JTAG circuit of the FPGA has been verified. It can be connected by opening the ChipScope, but it has been unable to connect now. The JTAG of the FPGA passes through a 244 buffer chip. The circuit is as follows. The line on the right side of 244 is directly connected to the corresponding pin of the FPGA. superior.

Why can't the TI DSP be connected? The problem that the JTAG interface cannot be connected

I tried many times but still couldn't connect, and I was a little desperate. Later, I couldn't do anything, so I just tested the JTAG pins, but it didn't turn on the power. The result was that there was a problem. TDO was actually shorted to ground. , what's going on, J10 is a single row of pins and there will be no problem, it can only be 244 broken, well, so I replaced a SN74LVTH244 ADBR , everything is OK!

My inspiration from this question is: if it can't be connected all the time, it is very likely that there is a problem with the hardware circuit! !