Burn the program into the FPGA chip with USB blaster, and the prompt is “error: can’t access JTAG chain”, and then the test JTAG chain still prompts this problem. After looking for the information on the Internet, I summarized the reasons for the prompt of “can’t access JTAG chain” when downloading. The common reasons are as follows:

(1) The selected FPGA model is inconsistent with the hardware;

(2) The communication between the parallel port and the download line is faulty or the download line is broken;

(3) Poor contact between download cable and JTAG socket;

(4) The JTAG port of the download line and the board is connected reversely;

(5) FPGA burned;

(6) Power supply problems;

(7) There is a problem with the schematic design;

(8) The large pad at the bottom of the FPGA chip is not grounded.
my problem is 4.
I’m ashamed. In fact, try the opposite and find the position of the first JTAG pin (small semicircle).

USB blaster user manual