EM6580SO14A EMMICRO [EM Microelectronic - MARIN SA], EM6580SO14A Datasheet - Page 12

• Manufacturer Part Number: EM6580SO14A
• Description: Ultra Low Power 8-pin Flash Microcontroller
• Manufacturer: EMMICRO [EM Microelectronic - MARIN SA]

5. Oscillator and Prescaler
5.1 RC Oscillator or external Clock
EM6580 can use the internal RC oscillator or external clock source for its operation.
The built-in RC oscillator without external components generates the system operating clock for the CPU and
peripheral blocks. The RC oscillator is supplied by the regulated voltage.
The RC oscillator frequency can be chosen from 5 possibilities with a register with 2 basic frequencies.
These are typically 32kHz, 64kHz, 128kHz, 256kHz or 500kHz for 32kHz basic frequency or 50kHz, 100kHz,
200kHz, 400kHz or 800kHz for 50kHz basic frequency . Depending on the selected RC frequency. A special 4
stage freq. divider is available to be able to deliver to Prescaler which generates all System clock except CPU
clock, a frequency close to 32 or 50 kHz to keep the peripheral timing as close as possible to specifications.
After POR the circuit always starts with the internal RC oscillator, but it can be switched to the external clock by
setting the ExtCPUclkON bit in the register RegPresc. The external clock is input at PA[1] and must be in
range from min. 10Khz to max. 1MHz. With this external frequency input all timing for peripherals change and
the special 4 stage freq. divider must be adapted to best suit the applied external frequency to keep 32/50kHz
System clock as close as possible. The system clock must be less than 64kHz. The external clock source
must be a square wave with full amplitude from V
depending on the external clock frequency.
Switching from internal RC oscillator to External clock or back from External clock to RC oscillator is made
without generating a glitch on the internal clock. Once the circuit is running on the external Clock one can
disable the RC oscillator by setting the RCoscOff bit in RegSCntl2 to ‘1’.
In sleep mode the oscillator is stopped. It can be stopped also by setting the RCoscOff bit. This bit can be set
only if ExtCPUClkOn was set before, indicating that the CPUck was switched from the internal RC oscillator to
the external clock which MUST be present. If the External Clock stops without going into Sleep mode first the
EM6580 can block and only POR can reset it.
Figure 8. below shows the connection of the RC oscillator and external clock and generation of CPUclk and
System clock = SysClk which is divided by the special 4 stage Freq. Divider if needed as described in
prescaler described in 5.3.
Figure 6. Clock source for CPU or system peripherals
Copyright © 2006, EM Microelectronic-Marin SA
PA[1]
metal option selection
32kHz – 512kHz
50kHz - 800kHz
R
RC oscillator
External clock
10kHz – 800kHz
ExtCPUclkON
SysClk = 32kHz or 50kHz
Automatic clock selection
depending on selected
RCClk
RCClk selection
1
0
MUX
Frequency
MUX
divider
ss
SysClk
to V
12
dd
. See Table 5.2.2 for advised special divisions
PRESCALER
LOW 15 stages divider Ck[15:1]
Ck[14]
CpuClk
SysClk
Ck[12]
Ck[1]
foutSel[1:0]
PAout[5]
PAout[2]
ResSys
Sout
MUX
MUX
MUX
www.emmicroelectronic.com
EM6580
To Peripherals
Ck[15:1]
CPUclk
5 .2 and
9 4 H
PA[5]
PA[2]