Reset_b pin oscillating - MK40

[Madsen]

Hi All,

I have two new boards I just build with the MK40.

I measure 3.3V on all power pins powered from an LM1117-3V3 together with 5V on the VREG pin from a LM1117-5.0V regulator.

Both chips are brand new and both exhibits square wave oscillation on the RESET_b pin and I have never managed to program them.

My debugger (UlinkPRO) can connect to the parts alright however I cannot flash any of them without getting a memory error.

I've read on this forum that other people have seen the same problem but I cannot seem to find a cure.

I have lots of decoupling capacitors (1nF // 100pF // 100nF so forth) around the chip as well as good electrolytes which ensures literally no ripple voltage on my supplies (i've tried removing the electrolytes as well to give a faster ramp up on the psu without effect)

I have tried an external 2.5V reset monitor tied directly to the Reset_b pin without luck

I have tried powering the chip via it's own 3.3V regulator (by hacking my pcb) this did not help either

Holding Reset_b low a few seconds while powering up and then releasing it doesnt do anything either so it doesnt seem to be related to POR ramping

Any ideas !?

/Lasse

[R_L_]

I think I'm having the same situation (oscillating reset_b),  but to hold the reset_b to gnd during the powerup doesn't put the MCU in program mode.

I send a picture of the reset pin .

Im using Keil + U-Multilink + KL05Z. Does anybody has any idea to put this device into program mode ???

[sahlisami]

Hi All,

I got the same problem with Kinetis KV10 ( MKV10Z32VLC7 device ) ; The reset pin is oscillating and my program couldn't run in stand alone mode without debugger ( I'm using JLINK with IAR IDE) .can you hlep me please ?

[martinzhang]

Hi Guys,

I use KV30F, IDE is IAR 7.4, J-Link-ARM, I got the same problem, the MCU can only work in debug mode, after power on, the reset pin is oscillating. I got some tips from above reply and tried following action then solved this problem:

1> Use J-Link Commander (V4.9b) connect to the MCU, use unlock Kinetis command to unlock the device

2> Use J-Link-ARM download the code to the MCU again

Hope this can help.

[apanecatl]

The behavior you are all seeing is due to the watchdog status of the microcontrollers, before they leave the factory, every microcontroller's watchdog is enabled, therefore they will not allow you to program them since the watchdog is continuously resetting the device, while the reset cycle is being performed the Reset_b pin will act as a POR, if you show the signal in an oscilloscope you will see a sawtooth signal. It is perfectly normal, in order to program the mcu you need to drive Reset_b low and then power up the mcu, this will break the reset cycle, prevent the watchdog from executing and forcing the mcu into EZ programming mode, where you can program it normally, this only needs to be done once.

[mayraramirez]

Hi Pedro 

There will be a way to perform this procedure by software? I'm using an external mcu KW41z In IAR with a P & E multilink

[keithtang]

Thanks Pedro. Apparently I was mislead to believe that was the culprit and apparently it was not.

[Madsen]

Hi Guys,

Updating KEIL uVision to the latest version solved everything for me !

So it seems it's someting to do with the ulinkpro !

[PhilH]

I had a similar problem with 3 of 5 prototype boards with a K60 on them.  The solution was to upgrade the firmware for my J-Link-ARM device (hardware rev 8.0) from 4.52c to 4.54.  There was a fix that as I understand it was to handle the problem with the watchdog timer being active at reset (but with no code to handle the watchdog timeout).  All I know is now I can program those 3 boards where I could not before.  This might be your problem as the symptom you describe matches what I saw.

Phil Hochstetler

[keithtang]

Thanks, Phil. Unfortunately I do not have J-Link. I am using Multilink instead. Will check if they have latest firmware that supprot this.

Anyway, just for my curiosity, how is this problem overcome by a programming tool?

[keithtang]

I am having the same problem with my MK60 (mask code 1N96B) chips. It is oscillating at 1.45 KHz (sawtooth wave). I tried all suggestions given by other members, such as holding the reset pin while powering up, reduce the power up slew rate, pull the EZ_CS pin high, etc without success.

I need the solution urgently, please can someone help.

Thanks.