MPC5604B/C Microcontroller Reference Manual, Rev. 8
100 Freescale Semiconductor
the test flash memory value is not visible at SIRC_CTL[SIRCTRIM] and this field shows a value of zero.
Therefore, be aware that the SIRC_CTL[SIRCTRIM] does not reflect the current trim value until you have
written to this field. Pay particular attention to this feature when you initiate a read-modify-write operation
on SIRC_CTL, because a SIRCTRIM value of zero may be unintentionally written back and this may alter
the SIRC frequency. In this case, you should calibrate the SIRC using the CMU or be sure that you only
write to the upper 16 bits of this SIRC_CTL.
In this oscillator, two's complement trimming method is implemented. So the trimming code increases
from –16 to 15. As the trimming code increases, the internal time constant increases and frequency
reduces. Please refer to device datasheet for average frequency variation of the trimming step.
6.5.3 Register description
Address: 0xC3FE_0080 Access: Read/write
0123456789101112131415
R00000000000
SIRCTRIM
W
RESET:
0000000000000000
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
R
000
SIRCDIV
000
S_SIRC
000
SIRCON_STDBY
W
RESET:
0000001100000000
Figure 6-4. Low Power RC Control Register (SIRC_CTL)
Table 6-6. SIRC_CTL field descriptions
Field Description
SIRCTRIM SIRC trimming bits.
This field corresponds (via two’s complement) to a trim factor of –16 to +15.
A +1 change in SIRCTRIM decreases the current frequency by
SIRCTRIM
(see the device data
sheet).
A –1 change in SIRCTRIM increases the current frequency by
SIRCTRIM
(see the device data
sheet).
SIRCDIV SIRC clock division factor.
This field specifies the SIRC oscillator output clock division factor. The output clock is divided
by the factor SIRCDIV+1.
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