NXP Semiconductors MC9S12G - Page 382

S12 Clock, Reset and Power Management Unit (S12CPMU)
MC9S12G Family Reference Manual Rev.1.27
384 NXP Semiconductors
Figure 10-25. IRC1M Frequency Trimming Diagram
Table 10-22. CPMUIRCTRIMH/L Field Descriptions
Field Description
15-11
TCTRIM[4:0]
IRC1M temperature coefficient Trim Bits
Trim bits for the Temperature Coefficient (TC) of the IRC1M frequency.
Figure 10-26 shows the influence of the bits TCTRIM4:0] on the relationship between frequency and
temperature.
Figure 10-26 shows an approximate TC variation, relative to the nominal TC of the IRC1M (i.e. for
TCTRIM[4:0]=0b00000 or 0b10000).
9-0
IRCTRIM[9:0]
IRC1M Frequency Trim Bits — Trim bits for Internal Reference Clock
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 bits IRCTRIM[9:6] can be done with frequency leaps of about 6% in average.
A fine trimming controlled by the bits IRCTRIM[5:0] can be done with 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 10-25 shows the relationship between the trim bits and the resulting IRC1M frequency.
IRCTRIM[9:0]
$000
IRCTRIM[9:6]
IRCTRIM[5:0]
IRC1M frequency (IRCCLK)
600KHz
1.5MHz
1MHz
$3FF
......