KL05 reset line problem?

[Frost]

I have a KL05Z32VLF4, 48pin LQFP package MCU. I've used the freedom boards, both KL25 and KL05 successfully with SDA and SWD using a segger j-link.

So, I have a custom board with the KL05Z32VLF4 on, the reset line is pulled to 3v3 with a 10K resistor, there is a 100nF cap to ground, and a switch across the cap. Due to an oversight I didn't put a series resistor in there, so had to remove the cap for the JTAG to connect up ok. The JLink connects and can debug a program, but the reset line is low when the JLink is not connected.

The 10K resistor manages to pull the reset line up to 0.3V without the cap, but I measured 1.5V with the 100nF in. As I write this, looking at the KL05 schematic, I can see a 1uF in the circuit, so I'm off to try a larger value of cap; could this be it?

Why is the reset line so low, has anyone else had this problem? What's wrong with my reset circuitry (apart from missing series resistor perhaps) I can find no shorts / open circuits in this area. Chip operates ok otherwise when reset is driven by JLink.

Thanks for any tips.

[Hui_Ma · Accepted solution]

Hi,

How do you measured 1.5V with voltage meter or with scope? If there with no code programmed in KL05 Flash, which could generate the invalide instruction reset and with scope you could measure the pulse signal.every 45us. You could use scope to measure the KL05 reset pin signal if there with pulse output.

Thank you.

B.R.

Ma Hui

[TurboMan]

Thanks Hui_Ma,

     that's probably what was happening. (this is my work account btw, Frost is me also.) I was using a meter, not a scope. when I removed the cap, the JLink could connect ok and debug, so I flashed a blank project on.

After I flashed code on, it worked ok. I also took the opportunity to put in a serial resistor to the reset line (same as previous PIC mcu designs). I'll mark this fixed from my other account when I get the chance! :smileyhappy: