56F802 Technical Data, Rev. 9

22

Freescale Semiconductor

Figure 3-6 Flash Mass Erase Cycle

3.5 Clock Operation

The 56F802 device clock is derived from an on-chip relaxation oscillator. The internal PLL generates a

master reference frequency that determines the speed at which chip operations occur.

The PRECS bit in the PLLCR (phase-locked loop control register) word (bit 2) must be set to 0 for internal

oscillator use.

3.5.1

Use of On-Chip Relaxation Oscillator

The 56F802 internal relaxation oscillator provides the chip clock without the need for an external crystal

or ceramic resonator. The frequency output of this internal oscillator can be corrected by adjusting the 8-bit

IOSCTL (internal oscillator control) register. Each bit added or deleted changes the output frequency of

the oscillator allowing incremental adjustment until the desired frequency is achieved. Figures 9 and 10

show the typical characteristics of the 56F802 relaxation oscillator with respect to temperature and trim

value.

During factory production test, an oscillator calibration procedure is executed which determines an

$103F in the Data Flash Information Block and recalled during a trim routine in the boot sequence

(executed after power-up and RESET). This trim routine automatically sets the oscillator frequency by

programming the IOSCTL register with the optimum trim value.

XADR

YE=SE=OE=0

ERASE

NVSTR

Tnvs

Tnvh1

Trcv

Tme

MAS1

IFREN

XE