JTAG Question - RESOLVED - Page 1
Forum section: electronics / beginners

author: Mr Transistor
author_rank: Newbie
timestamp: November 06, 2022, 04:43:30 pm
content: Hello,I want to write my own firmware for a device based on the TI TM4C123G (an ARM Cortex M4 MCU). I have a question I am hoping someone is willing to help me with. What type of connector do I need to connect my J-LINK PLUS to the JTAG port on the board in this picture?Thank you in advance for your advice!!Manny

author: DC1MC
author_rank: Super Contributor
timestamp: November 06, 2022, 04:48:53 pm
content: Is a type of JST connector, the exact type is difficult to find from the picture (it the pin aperture 0.1" or 0.05", or 2.0mm or...) but you may find some help here wit the exact model number:https://www.mattmillman.com/info/crimpconnectors/common-jst-connector-types/Also there are some JST connector kits on EBAY, you may find something suitable.Cheers,DC1MC

author: Mr Transistor
author_rank: Newbie
timestamp: November 06, 2022, 05:03:56 pm
content: My apologies for the low picture quality in my first post. I hope this picture is more helpful.

author: wasedadoc
author_rank: Super Contributor
timestamp: November 06, 2022, 05:11:02 pm
content: You also need to know which pins are which.

author: DC1MC
author_rank: Super Contributor
timestamp: November 06, 2022, 05:14:59 pm
content: Quote from: Mr Transistor on November 06, 2022, 05:03:56 pmWell, it may be a PH series, but you have to manually measure the aperture (distance between pins center) and then waste hours digging trough datasheets, do understand that there are hundreds if not thousands of models, not to mention the custom orders. JST are the cancer of connectors world

author: Mr Transistor
author_rank: Newbie
timestamp: November 06, 2022, 07:14:37 pm
content: Quote from: wasedadoc on November 06, 2022, 05:11:02 pmThat is an excellent point I hadn't thought of quite yet. I suppose I will have to follow the traces to the MCU with my DMM (I am assuming it is more than a 2 layer board)? Then consult the MCU pinout in the data sheet?

author: Mr Transistor
author_rank: Newbie
timestamp: November 06, 2022, 07:19:06 pm
content: Quote from: DC1MC on November 06, 2022, 05:14:59 pmI agree. Maybe I am just naive but I don't understand why so many wire to board connectors are needed. But what do I know.Because this is just for hobby, if I can't source the connector I may just hack something together. I appreciate the help.

author: RoGeorge
author_rank: Super Contributor
timestamp: November 06, 2022, 07:27:43 pm
content: While ports and other pins can be remapped to various physical pins, the JTAG pins in a chip will never change.First, identify the GND pin in the connector, either visually or with a DMM (on continuity).Same to identify the Vcc pin in the connector.Then, look in the MCU datasheet and probe with the DMM for continuity between the MCU JTAG pin and the remaining pins from the connector, to identify which MCU JTAG pin goes where in the connector.This might help if you want to write your own JTAG software, or want to know why 6 pins in the JTAG connector:https://www.fpga4fun.com/JTAG.html

author: Mr Transistor
author_rank: Newbie
timestamp: November 06, 2022, 07:54:00 pm
content: Quote from: RoGeorge on November 06, 2022, 07:27:43 pmThank you for the steps. I had no idea that the JTAG pins are discrete.

author: Mr Transistor
author_rank: Newbie
timestamp: November 06, 2022, 07:55:16 pm
content: I think I figured it out. It appears to be the below Molex part. What lead me toward Molex was the color of the plastic just wasn't the "JST white" I am familiar with. I appreciate everyone's help!https://www.molex.com/molex/products/part-detail/pcb_headers/0533980671#