ATAR862-3 Datasheet, PDF (26/105 Pages) ATMEL Corporation – Microcontroller with UHF ASK/FSK Transmitter

External Input Clock
Figure 22. RC-oscillator 1
RC
oscillator 1
RcOut1
Stop
RcOut1
Osc-Stop
Control
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
external 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.
Figure 23. External Input Clock
Ext. ^OSC1
Clock
or
Ext. ^OSC2
Clock
Ext. input clock
ExIn
ExOut
Stop
Clock monitor
RcOut1
Osc-Stop
CCS
Res
OS1
1
1
x
OS0
1
1
0
CCS
0
1
x
Supervisor Reset Output (Res)
Enable
Disable
Disable
RC-oscillator 2 with External
Trimming Resistor
The RC-oscillator 2 is a high resolution trimmable oscillator whereby the oscillator fre-
quency can be trimmed with an external resistor between OSC1 and V_DD. In this
configuration, the RC-oscillator 2 frequency can be maintained stable with a tolerance of
± 10% over the full operating temperature and a voltage range V_DD from 2.5 V to 6.0 V.
For example: An output frequency at the RC-oscillator 2 of 2 MHz can be obtained by
connecting a resistor R_ext = 360 kW (see Figure 16).
26 ATAR862-3
4556B–4BMCU–02/03