Chapter 4 Clock Description
MPC5602P Microcontroller Reference Manual, Rev. 4
Freescale Semiconductor
99
If F
SYS_CLK
is less than a reference value determined by the CMU_1_LFREFR_A[LFREF_A] bits and
the system clock is enabled, then:
•
CMU_1_ISR[FLLI] is set
•
A failure event is signaled to the MC_RGM and FCU, which in turn can generate a ‘functional’
reset, a SAFE mode request, or an interrupt
NOTE
The system clock monitor may produce a false event when F
SYS_CLK
is less
than 2
F
IRCOSC_CLK
/2
CMU_1_CSR[RCDIV]
due to an accuracy limitation of
the compare circuitry.
4.9.3.4
Frequency meter
The frequency meter calibrates the internal RC oscillator (CK_IRC) using a known frequency.
NOTE
This value can then be stored into the flash so that application software can
reuse it later on.
The reference clock will be always the XOSC. A simple frequency meter returns a draft value of CK_IRC.
The measure starts when bit SFM (Start Frequency Measure) in the CMU_CSR is set to ‘1’. The
measurement duration is given by the CMU_MDR in numbers of IRC clock cycles with a width of 20 bits.
Bit SFM is reset to ‘0’ by hardware once the frequency measurement is done and the count is loaded in the
CMU_FDR. The frequency f
RC
can be derived from the value loaded in the CMU_FDR as follows:
f
RC
= (f
OSC
× MD) /
n
Eqn. 4-12
where
n
is the value in the CMU_FDR and MD is the value in the CMU_MDR.
4.9.4
Memory map and register description
shows the memory map of the CMU.
Table 4-10. CMU memory map
Offset from
CMU_BASE
(0xC3FE_0100)
Register
Access
Reset value
Location
0x0000
Control Status Register (CMU_0_CSR)
R/W
0x0000_0006
0x0004
Frequency Display Register (CMU_0_FDISP)
R
0x0000_0000
0x0008
High Frequency Reference Register FMPLL_0
(CMU_0_HFREFR_A)
R/W
0x0000_0FFF
0x000C
Low Frequency Reference Register FMPLL_0
(CMU_0_LFREFR_A)
R/W
0x0000_0000
0x0010
Interrupt Status Register (CMU_0_ISR)
R/W
0x0000_0000
0x0014
Reserved