Freescale Semiconductor MPC5604B - Memory Map and Register Description

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MPC5604B/C Microcontroller Reference Manual, Rev. 8

114 Freescale Semiconductor

NOTE

If PLL frequency goes out of range, the CMU shall generate FMPLL fll/fhh

event. It takes approximately 5 s to generate this event.

6.8.4.3 Frequency meter

The purpose of the frequency meter is twofold:

• to measure the frequency of the oscillators SIRC, FIRC or SXOSC

• to calibrate an internal RC oscillator (SIRC or FIRC) using a known frequency

Hint: This value can then be stored into the flash so that application software can reuse it later on.

The reference clock is always the FXOSC_clk. The frequency meter returns a precise value of frequencies

SXOSC_clk

, f

FIRC_clk

or f

SIRC_clk

according to CKSEL1 bit value. 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 clock cycles of the selected clock source 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

can be derived from the value loaded in the CMU_FDR as follows:

= (f

FXOSC

× MD) / n Eqn. 6-1

where n is the value in the CMU_FDR and MD is the value in the CMU_MDR.

The frequency meter by default evaluates f

FIRC_clk

, but software can swap to f

SIRC_clk

or f

SXOSC_clk

programming the CKSEL bits in the CMU_CSR.

6.8.5 Memory map and register description

The memory map of the CMU is shown in Table 6-16.

1. x = FIRC,SIRC or SXOSC

Table 6-16. CMU memory map

Base address: 0xC3FE_0100

Control Status Register (CMU_CSR) 0x00 0x00000006 on page 115

Frequency Display Register (CMU_FDR) 0x04 0x00000000 on page 116

High Frequency Reference Register FMPLL (CMU_HFREFR) 0x08 0x00000FFF on page 116

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