Richard Serge

Questions about S08ICSV3 (MC9S08QEx) Clock Generator

Discussion created by Richard Serge on Oct 28, 2011
Latest reply on Oct 29, 2011 by Richard Serge

My objective is to get a fast stable BUSCLK (internal osc) from a QE8 as simple as possible. This is what I've read in AN3499 (Clock Options on the HC9S08 Family) about the ICS in section 2.1:


Table 4 shows that with DRS bits = 00 and DMX32=1 that I get a reference freq of 32.768K and a DCO output freq of 19.92M, which can give me a BUSCLK of 9.96M. It also states in section (about the ICS Status & Control reg) that


"The register also contains the DCO maximum frequency bit (DMX32) that determines if a finely tuned reference frequency of 32.768 kHz is used. When using this reference, the DCO multipliers are greater when compared to general reference frequencies and this provides a fixed DCO output."


When I read "a finely tuned reference frequency..." it made me wonder WHO does this "finely tuned" thing, me via the trim bits, or Freescale in the chip? Table 4 makes me think it is independant of the trim bits.


Anyone have any experience using it this way?