SolderSplash Labs Forum

Hi,
We are using the wait_us mbed library function, and it doesn't seem to count accurately in micro-seconds.
It seems to be 20% slow. i.e wait_us(10) delays for 12 uS.
We would like to check the pre-scaler values in the mbed library, but need to know the crystal oscillator frequency to do this.
Thanks for your help.
Giles H

Hi Giles,

Input xtal freq is 12mhz, I shall have a look at the wait functions to see If i can see what is happening

I've done a quick test of the wait function by toggling a port pin so that I could read the result on my scope & logic analyser.

Test 1 : using the DigitalOut class I get 11.31us between edges
Test 2 : using direct port control, the NOT register will toggle the port pin, LPC_GPIO->NOT[ 1 ] = 1<<22; I get 10.96us between edges
Test 3 : Reduced wait to wait_us(9) I now get between 9.38us-10.13us between edges

So seems okay, not wildly out, accurate flexible delay functions are quite hard.

What is the reason for the delay, what are you trying to achieve?

Hi Carl,
Apologies for the slow response.
wait_us(9) should be fine.
To answer your question, our Chinese manufacturer builds remote control lights, and we are making a WiFi DMX512 control board to integrate into their products. We need async serial, but with more control than a standard UART.
They make these www.eliminata.com for us
BTW is the board 5V input @ pin 32 and 3.3V Output at Pin 11. I assume you can't put 3.3V in at Pin 11?
Thank you for your support.
Great product, happy to recommend it if anyone asks.
cheers
Giles H

Hi Giles,

I have implemented DMX512 on both the M0/M3. Although I cheated and used NXP's app note They use a timer for the delay for the MAB.

We have made an LPC DMX512 board but so far haven't made it available.

Here is the NXP app note : http://www.nxp.com/applications/lightin ... sign-tools

Carl.

"is the board 5V input @ pin 32 and 3.3V Output at Pin 11. I assume you can't put 3.3V in at Pin 11?"

Yes you can supply the board 5v's or 3.3v using those pins.