Rainbow Electronics ATAR862-3 - Manual (Page 26)

26
ATAR862-3
4556B–4BMCU–02/03
Figure 22. RC-oscillator 1
External Input Clock 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
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 k W (see Figure 16).
RC
oscillator 1
RcOut1
Stop
Control
RcOut1
Osc-Stop
OS1 OS0 CCS Supervisor Reset Output (Res)
1 1 0 Enable
1 1 1 Disable
x 0 x Disable
Ext. input clock
ExOut
Stop
Ext.
Clock
RcOut1
Osc-Stop ExIn
CCS
Res
OSC1
OSC2
Clock monitor
Ext.
Clock
or