by Frida » Thu Jul 17, 2014 1:03 pm
1: First I power up my board and waited until the login screen was on, then I hit the reset button shortly and waited until the login screen was on again. Now I could login.
2: I tried to hold the reset button for 10 sec. until I was sure that power on the card had stabilized. It did not help.
3: Then I found out, when I hit the reset button when the USER LED came on, then I could login.
4: I looked on the datasheet of U33, and saw that the output on pin 4 is high Z, when there is no power. It meant that the BOARD_RESET is not in reset at the moment we power up. I then took my needle and resistance and place it on pin 4 and ground and then power up. As soon the USER LED came on, I removed my needle and I could login.
5: That made my think of a rc delay on PIN 4, but before I did it, I measured the voltages on the USER LED and measured 3.16 volts on pin 2 and 1.22 volts on PIN 1. I saw that the resistance R30 was 230 ohm., so that in serie with R295 1k ohm., could held the reset ontil the USER LED came on. The 1.22 volt is high enough to get it out af reset and still under 1.8 volts that is max. So I could not resist placing a jumper from U33 PIN 4 to CR 10 PIN 1.
6: And yes, it works fine for me. Now I can held down the reset button as long as I wish, and it will still start up, when I release it.
And yes, that is what a reset button should do.
I thought with my powersupply it will take several usec. to power up all the circuits,
and which circuit has enough voltage to operate first, maybe the reset circuit come in with a reset pulse after some circuits has begun to work.
@FHuettig, Are You always using a bench powersupply, maybe it is strong enough to rapidly power on the circuit, so that you dont se our problems:)
What does TURBO_MODE?, it is high when powered from J12, and low when I change the jumper to power it from USB_VBUS.
Please ask again if there is something not to understand.