Clock Generation Overview
6.4 Clock Generation Overview
The SIM uses the master clock (2X system clock) at a maximum of 64MHz from the OCCS module to
produce a system clock at a maximum of 32MHz for the peripheral, core, and memory. It divides the
master clock by two and gates it with appropriate power mode and clock gating controls. A 3X system
high-speed peripheral clock input from OCCS operates at three times the system clock at a maximum of
2
96MHz and can be an optional clock for PWM, Timer A, and I C modules. These clocks are generated by
gating the 3X system high-speed peripheral clock with appropriate power mode and clock gating controls.
The OCCS configuration controls the operating frequency of the SIM’s master clocks. In the OCCS, either
an external clock (CLKIN), a crystal oscillator, or the relaxation oscillator can be selected as the master
clock source (MSTR_OSC). An external clock can be operated at any frequency up to 64MHz. The crystal
oscillator can be operated only at a maximum of 8MHz. The relaxation oscillator can be operated at full
speed (8MHz), standby speed (200kHz using ROSB), or powered down (using ROPD). An 8MHz
MSTR_OSC can be multiplied to 196MHz using the PLL and postscaled to provide a variety of high-speed
clock rates. Either the postscaled PLL output or MSTR_OSC signal can be selected to produce the master
clocks to the SIM. When the PLL is selected, both the 3X system clock and the 2X system clock are
enabled. If the PLL is not selected, the 3X system clock is disabled and the master clock is MSTR_OSC.
In combination with the OCCS module, the SIM provides power modes (see Section 6.5), clock enables,
and clock rate controls to provide flexible control of clocking and power utilization. The clock rate
controls enable the high-speed clocking option for the two quad timers (TMRA and TMRB) and PWM,
but requires the PLL to be on and selected. Refer to the 56F802X and 56F803XPeripheral Reference
Manual for further details. The peripheral clock enable controls can be used to disable an individual
peripheral clock when it is not used.
56F8036 Data Sheet, Rev. 6
Freescale Semiconductor
107
FREESCALE [ Freescale ]
