ATAM862 datasheet(26/110 Pages) ATMEL

26 / 110 page

4554E–4BMCU–05/06

ATAM862-3

Figure 18-2. Internal Supply Voltage Supervisor

Figure 18-3. External Input Voltage Supervisor

19. Clock Generation

19.1

Clock Module

The ATAM862-3 contains a clock module with 4 different internal oscillator types: two RC-oscil-

lators, one 4-MHz crystal oscillator and one 32-kHz crystal oscillator. The pins OSC1 and OSC2

are the interface to connect a crystal either to the 4-MHz, or to the 32-kHz crystal oscillator.

OSC1 can be used as input for external clocks or to connect an external trimming resistor for the

RC-oscillator 2. All necessary circuitry, except the crystal and the trimming resistor, is integrated

on-chip. One of these oscillator types or an external input clock can be selected to generate the

system clock (SYSCL).

In applications that do not require exact timing, it is possible to use the fully integrated RC-oscil-

lator 1 without any external components. The RC-oscillator 1 center frequency tolerance is

better than

± 50%. The RC-oscillator 2 is a trimmable oscillator whereby the oscillator frequency

can be trimmed with an external resistor attached between OSC1 and V

DD. In this configuration,

the RC-oscillator 2 frequency can be maintained stable with a tolerance of

± 15% over the full

operating temperature and voltage range.

The clock module is programmable via software with the clock management register (CM) and

the system configuration register (SC). The required oscillator configuration can be selected with

the OS1 bit and the OS0 bit in the SC register. A programmable 4-bit divider stage allows the

adjustment of the system clock speed. A special feature of the clock management is that an

external oscillator may be used and switched on and off via a port pin for the power-down mode.

Before the external clock is switched off, the internal RC-oscillator 1 must be selected with the

CCS bit and then the SLEEP mode may be activated. In this state an interrupt can wake up the

controller with the RC-oscillator, and the external oscillator can be activated and selected by

software. A synchronization stage avoids too short clock periods if the clock source or the clock

speed is changed.

Low threshold

Middle threshold

High threshold

VMS = 1

Low threshold

Middle threshold

High threshold

VMS = 0

3.0 V

2.6 V

2.2 V

1.3 V

VMI

VMS = 1

VMS = 0

Positive slope

Negative slope

VMS = 1

VMS = 0

Interrupt negative slope

Interrupt positive slope

Internal reference level

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