ST72521 does not work with correct frequency

[thilo]

Posted on May 22, 2003 at 08:16

ST72521 does not work with correct frequency

[thilo]

Posted on May 22, 2003 at 05:27

Hello,

I work with the ST72521 and I use a crystal with a 8Mhz clock frequency. I always measure on the MCO-Pin a frequency of 3MHz. I think that my adjustments on the option bytes are correctly. The design of my target board is correctly too, I think. Is it possible that the microcontroller works with the internal clock and he ignores all my adjustments? I have no idea what the problem is. thilo

[itsmejatinus]

Posted on May 22, 2003 at 08:16

Hello,

I think the clock that you are getting is CSS clock(~3MHz). It comes to operation if your resonator oscillator ckt is disconnected or is not working. So check for the resonator oscillator connections & also make sure that crystal is ok.