what is the oscillation frequency to this microcontroller?

[sknoogleplex]

Hi, I'm a grad student working a project using an LPC2148 microcontroller. I need to know what the oscillation frequency of its (external) clock is. This is the board I'm using, and here is the corresponding **broken link removed**. You can see the input for the clock, RTCX1, at the center left pin of the chip as drawn. There is also an oscillator right there labelled "Q2 32768".

This label led me to believe the oscillator frequency was 32.786 kHz or 32768 kHz, but page 18 in the manual for my mcu (LPC2148) says "this microcontroller's internal oscillator circuit supports external crystals in the range of 1 MHz to 30 MHz only". Do I need to be doing some computation with the capacitors as well? Could you explain what I'm missing?

(To clarify and ensure that I'm understanding the manual, the frequency I'm trying to find is F_OSC from page 18 of the mcu manual.)

(I'm a total newb to this stuff, obviously. Thanks a lot for your help.)

Ryan

 

[sknoogleplex]

Less critical question: page 18 in the manual also says two modes are possible "slave mode" and "oscillation mode". However, I can't find anywhere that it explains how the mode is determined. Does anyone else see it? Is it chosen by hardware or software?

Thanks very much, again.

 

[sknoogleplex]

Ah, there is another crystal. 12 MHz.

Got it. So... does anyone know what determines if this is using the internal or external oscillator? (As mentioned above, page 18 of the manual starts discussing these two modes - slave mode and oscillator mode - but I can't find anywhere that says how the mode is determined.) Thanks.

 

[futz]

This label led me to believe the oscillator frequency was 32.786 kHz or 32768 kHz,

That 32.768KHz crystal is for the RTC.

The other 12MHz crystal is the one for the processor.