JTAG connection - resistors

stankovic · ‎2008-02-08

Posted on February 08, 2008 at 15:09

16-32micros · ‎2011-05-17

Posted on May 17, 2011 at 12:23

Dear maestral, Ivan,

You are completly right, we have embedded these resitors internally on STM32 so you can just connect the STM32 JTAG or SWD Pins to your connector, The evaluation board was made before having the STM32 silicon and follwing Standard JTAG schematics commonly used in the Market at that time. Now, with STM32 you do not need these extra Pull-up/down resistors and you can save PCB cost 🙂 Cheers,

STOne-32

stankovic · ‎2011-05-17

Posted on May 17, 2011 at 12:23

Hello,

I found ST ARM CORTEX family really exciting and I am working on sch of prototype.

One thing confuse me- it is written in datasheet that there are weak pull-up resistors (40K typical) on JTAG pins (which is great feature) but in spite of this all dev. board sch I could see (including ST board)there are 10K resistors placed.

Do I really need those resistors?

ivan239955_stm1_st · ‎2011-05-17

Posted on May 17, 2011 at 12:23

When I build my board, I relied on STM32 pull-ups on JTAG pins.

I haven't used any external pull up resistors.

My JTAG works just fine at full speed (Wiggler JTAG, 400 kHz clock).

Adding external pull-ups on ST board can be likely explained by designers habit - they are required on most other processors. External pull-up won't hurt, maybe they are improving signal integrity for higher JTAG clock frequencies (few MHz).

Ivan