AnsweredAssumed Answered

Reset issue of on board K20DX128 of FRDM

Question asked by Kai Liu on Sep 17, 2014
Latest reply on Sep 25, 2014 by Kai Liu

It seems K/KL micro always bugs me a lot. I have solved reset issue of KL25 by a series resistor in SWD_CLK. Now it comes again, with slight differences.


RESET always LOW

I have a FRDM-K20 board. It worked well when it arrived as a new package, OpenSDA bootloader + CMSIS-DAP debugger/PEmicro debugger and MSD programmer. Also I have developed bootloader and firmware on that board as well.


Today I try to evaluate a new firmware. I can not connect it by Keil + CMSIS-DAP debugger + FRDM. The RESET pin keeps low.


However, since the on board K20 has been programmed by the demo firmware released from FSL. Yes, the demo code from Quick Start Package. It should not be an empty micro which makes reset by internal watchdog. I also found it is pulled low constantly, not reset over and over.


K20 is not DEAD

If I toggles debugger setting in Keil by toggling JTAG/SWD, the code runs a while, since the LED blanks. However, the CMSIS-DAP reports SWD/JTAG communication failure. I also use PEmicro Multilink, some issue.


Always in BOOTLOADER, Hard to enter CMSIS-DAP

Since RST line connects to K20 debugger micro, it enforced debugger K20 always into BOOTLOADER mode, not pre-programmed CMSIS-DAP mode. It happens all the morning. In the afternoon, it allows me to enter CMSIS-DAP. But the user K20 stills in reset mode.


Any ideas about this issue?

The reset line keeps on 0.5V DC. I also checked the push button, pull up resistor, capacitor. Only pull-up resistor is 103, 10K, but measured at 1K, I believe it has parallel resistor internally.