ATAR090-D Datasheet, PDF (15/70 Pages) ATMEL Corporation – Low-current Microcontroller for Wireless Communication

ATAR090-D
Oscillator Circuits and
External Clock Input Stage
RC-oscillator 1
Fully Integrated
The ATAR090-D 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.
For timing insensitive applications, it is possible to use the fully integrated
RC-oscillator 1. It operates without any external components and saves additional
costs. The RC-oscillator 1 center frequency tolerance is better than ±50% over the full
temperature and voltage range. The basic center frequency of the RC-oscillator 1 is
f₀ ≈ 3.8 MHz. The RC-oscillator 1 is selected by default after power-on reset.
Figure 15. RC-oscillator 1
External Input Clock
RC-oscillator 1
RcOut1
Stop
Control
RcOut1
Osc-Stop
The OSC1 or OSC2 (mask option) can be driven by an external clock source provided it
meets the specified duty cycle, rise and fall times and input levels. Additionally the exter-
nal clock stage contains a supervisory circuit for the input clock. The supervisor function
is controlled via the OS1, OS0-bit in the SC register and the CCS-bit in the CM-register.
If the external input clock is missing for more than 1 ms and CCS = 0 is set in the
CM-register, the supervisory circuit generates a hardware reset. The input clock has
failed if the frequency is less than 500 kHz for more than 1 ms.
Figure 16. External Input Clock
Ext. ^OSC1
Clock
or
Ext. _OSC2
Clock
Ext. input clock
ExIn
ExOut
Stop
Clock monitor
RcOut1
Osc-Stop
CCS
Res
4701C–4BMCU–12/04
Table 6. Supervisor Function Control Bits
OS1
1
1
x
OS0
1
1
0
CCS
0
1
x
Supervisor Reset Output (Res)
Enable
Disable
Disable
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