I've developed a prototype using the STM NUCLEO (NUCLEO-F411RE) board and now that I am happy with design I am now in the process of testing everything together on my own PCB. All the other components designed for on my PCB are working great except for the new bare STM32F411RE (LQFP4 package) I have integrated onto the board. I am unable to connect to the board via the SWD interface to upload any program and am now completely stumped after many debug attempts! I followed all the hardware design recommendations provided in the STM32 application notes, (https://www.st.com/content/ccc/resource/technical/document/application_note/76/f9/c8/10/8a/33/4b/f0/DM00115714.pdf/files/DM00115714.pdf/jcr:content/translations/en.DM00115714.pdf).
I tried using two different programmers to communicate with the board; 1) ST-Link/V2-ISOL 2) The ST-Link that can be broken of the NUCLEO board
I verified that both of the programmers work when connecting to the correct pins on the NUCLEO-F4llRE breakout board which is VDD/SWCLK(PA14)/GND/SWDIO(PA13)/NRST/SWO(PB3). The connection verification is done with the STM32 ST-Link Utility software. The settings for the ST-Link utility are; connection settings = SWD, freq = 480kHZ (I have tried other frequencies), mode = connect under reset and reset mode is Hardware reset.
When trying to connect I get the "can not connect to target!" error from the the ST-Link utility as well as a FAIL.txt from the ST-Link V2 which contains "the interface firmware FAILED to reset/halt the target MCU". I hooked up my oscilloscope to analyze the NRST pin which I have pulled high with a 10Kohm resistor along with a cap to ground near the STM32F4 reset pin. I see that the ST-Link is sending a reset pulse but the MCU but no connection I guess. I then tried connecting to the board by pulling NRST to low with a 10k pull-down resistor and still no connection... I checked the continuity between the STM32f4 pins on the PCB and the connector pins and everything is okay in terms of soldering I guess? I believe the layout and placement of the controller is correct as I followed the ST datasheet as well as NUCLEO board layout. Maybe if someone could verify that would be great! Also I am new to PCB dev with mcu's so this very well could be a stupid mistake I am not seeing :)
Also, I have my board powered from a separate power supply before connecting the ST-LINK V2 programmer. Any help/recommendations would be much appreciated as I am stuck! Here are some photos of my setup