STM8L: CCO pin

elil · ‎2011-09-06

Posted on September 06, 2011 at 22:27

Dear,

Working with Discovery board, I encountered the following problems with CCO pin:

1. When HSI(16MHz) is routed to CCO, the signal on the CCO

a. has a low and not stable amplitude from 500mV to 1.2V.

b. The signal is a triangle wave

c The signal has a DC offset

2. When LSI(38KHz) is routed to CCO,

a. instead of 38KHz I see 10Hz of RTC which sourced from LSI (or perhaps it is ok ?)

b. A lot of pulses are lost.

Regarding the problem 1 I got an answer from ST support, that 16 MHz is too fast and CCO can't drive it. With all respect to ST guy who gave me that answer, I'm not sure if the answer is correct, since if the pin can't drive 16MHz, why ST gave this ability ? Did somebody here encounter this problem too ?

The problem 2 is absolutely unclear for me.

Any idea would be highly appreciated.

Best Regards,

E.L.

Viktor POHORELY · ‎2011-09-07

Posted on September 07, 2011 at 16:12

Could you provide to me an information about register settings you have made, in order to know the setting you have used?

Did you configured GPIO into push pull mode?

The message below seems a bit missinterpreted - GPIO is capable to handle signals up to 2MHz, respectively 10MHz, depending on the GPIO configuration. Thus, you would not see a 16 MHz square signal, but a shape similar to a charging of capacitor...

elil · ‎2011-09-07

Posted on September 07, 2011 at 18:20

Dear Setler,

Thank you for you comment.

It's funny, while writing to you I rechecked the GPIO configuration and found PC4 pin, which is associated with CCO, was not configured - I left it floating. Since you mentioned Push-Pull pin configuration, I configured it as a such, and the problem disappeared.

Now I see nice 16MHz signal. I think the configuration of GPIO slope is not relevant in this case as CCO is not GPIO.

Best Regards,

E.L.