MC9S12P128 Datasheet, PDF (227/564 Pages) Freescale Semiconductor, Inc – S12 Microcontrollers

S12 Clock, Reset and Power Management Unit (S12CPMU) Block Description
Table 7-20. CPMUIRCTRIMH/L Field Descriptions
Field
Description
15,14,13,12
IRC1M temperature coefficient Trim Bits
These bits are to trim the temperature coefficient (TC) of the frequency of the IRC1M.
Figure 7-28 shows the influence of the bits TCTRIM3:0] on the relationship between frequency and temperature.
Figure 7-27 shows an approximate TC variation, relative to the nominal TC of the IRC1M (i.e. for
TCTRIM[3:0]=0000 or 1000).
9,8,7,6,5,4,3 IRC1M Frequency Trim Bits — Trim bits for Internal Reference Clock
,2,1,0 After System Reset the factory programmed trim value is automatically loaded into these registers, resulting in a
Internal Reference Frequency f_{IRC1M_TRIM}. See device electrical characteristics for value of f_{IRC1M_TRIM}.
The frequency trimming consists of two different trimming methods:
A rough trimming, controlled by the bits IRCTRIM[9:6], and allowing frequency leaps of about 6% in average.
A fine trimming, controlled by the bits IRCTRIM[5:0], and allowing frequency leaps of about 0.3% (this trimming
determines the precision of the frequency setting of 0.15%, i.e. 0.3% is the distance between two trimming
values).
Figure 7-26 shows the relationship between the trim bits and the resulting IRC1M frequency.
IRC1M frequency (IRCCLK)
1.5MHz
{ ^IRCTRIM[5:0]
1MHz
IRCTRIM[9:6]
......
600KHz
$000
Figure 7-26. IRC1M Frequency Trimming Diagram
IRCTRIM[9:0]
$3FF
S12P-Family Reference Manual, Rev. 1.12
Freescale Semiconductor
227