LPC4330 ngx xplorer board - Weird voltages registered at multiple pins using blinky project

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by verybadalloc on Wed Feb 24 22:59:14 MST 2016

I have been getting some really weird voltages on the xplorer ngx 4330 board, and I was hoping I would get some kind of explanation of what I doing wrong. I am using LPCXpresso 8.

I ran the blinky project from the examples provided with the Xpresso, and I am able to see that it runs (the LED is blinking). I then get the oscilloscope, and start probing each pin on the board. The obvious ones, like 5V and 3.3V report correct values. However, a large number of pins seem to be giving me values, even though I am not using them. For example:
- I get 0.7V on the pins GPIO5[7], GPIO0[9] and GPIO1[10]
- I get 3.3V on the pins GPIO0[8], GPIO1[9], GPIO0[7] and GPIO1[11]
- I get 3.1V on GPIO0[4], GPIO3[5], GPIO3[7], and GPIO31[1].

What is really frustrating is that these values don't seem to go away, even when I try to use these GPIO to write values from the MCU. For example, using the following code:

Chip_SCU_PinMuxSet(5, 7, SCU_PINIO_FAST); //5_7
Chip_GPIO_SetPinDIROutput(LPC_GPIO_PORT, 5, 7);
Chip_GPIO_SetPinOutHigh(LPC_GPIO_PORT, 5, 7);

I am still seeing the 0.7 V output at the pin.

The only pins that I can actually program to are GPIO0[2], GPIO1[12], GPIO5[0], GPIO0[3], GPIO0[1] and GPIO0[0].

Also, I had a second question with regards to generating a clock signal. Currently, the SCK pin outputs a clock signal at 204MHz, the frequency of the MCU. Is it possible to output a clock signal at 20MHz, on a different pin? I am thinking just a pin that changes state every 10 cycles.

Thanks again for your help!