ATAR862-4_07 Datasheet, PDF (27/112 Pages) ATMEL Corporation – Microcontroller with UHF ASK/FSK Transmitter

ATAR862-4
In this state an interrupt can wake up the controller with the RC-oscillator, and the external oscil-
lator 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.
If an external input clock is selected, a supervisor circuit monitors the external input and gener-
ates a hardware reset if the external clock source fails or drops below 500 kHz for more than
1 ms.
Figure 19-1. Clock Module
OSC1
*
OSC2
*
Oscin
Ext. clock
ExIn
ExOut
Stop
RC oscillator2
R_Trim
RCOut2
Stop
4-MHz oscillator
Oscin
Oscout
4Out
Stop
32-kHz oscillator
Oscout Oscin
Oscout
32Out
RC
oscillator 1
Stop
IN1
RCOut1
Control
IN2
Cin
/2
/2
/2
Divider
Osc-Stop
Sleep
WDL
CM: NSTOP CCS
CSS1 CSS0
*
mask option
SC: BOT - - - OS1 OS0
/2
Cin/16
32 kHz
SYSCL
SUBCL
Figure 19-2. Clock Modes
Clock Source for SYSCL
Mode OS1 OS0
CCS = 1
CCS = 0
1
1
1
RC-oscillator 1 (internal)
External input clock
2
0
1
RC-oscillator 1 (internal)
RC-oscillator 2 with
external trimming resistor
3
1
0
RC-oscillator 1 (internal)
4-MHz oscillator
4
0
0
RC-oscillator 1 (internal)
32-kHz oscillator
Clock Source
for SUBCL
C_in/16
C_in/16
C_in/16
32 kHz
The clock module generates two output clocks. One is the system clock (SYSCL) and the other
the periphery (SUBCL). The SYSCL can supply the core and the peripherals and the SUBCL
can supply only the peripherals with clocks. The modes for clock sources are programmable
with the OS1 bit and OS0 bit in the SC register and the CCS bit in the CM register.
19.2 Oscillator Circuits and External Clock Input Stage
The microcontroller block series consists of four different internal oscillators: two RC-oscillators,
one 4-MHz crystal oscillator, one 32-kHz crystal oscillator and one external clock input stage.
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4552H–4BMCU–07/07