WiFiDIP Cortex Crystal frequency

[GilesHutch]

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

[Carl-SolderSplash]

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

[Carl-SolderSplash]

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?

[GilesHutch]

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

[Carl-SolderSplash]

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.

[Carl-SolderSplash]

"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.