EM6603 EM Microelectronic, EM6603 Datasheet - Page 8

• Manufacturer Part Number: EM6603
• Description: Ultra Low Power Multi I/O Microcontroller
• Manufacturer: EM Microelectronic

4
A built-in crystal oscillator circuit generates the system operating clock for the CPU and peripheral circuits from an
externally connected crystal (typ. 32.768kHz) and trimmer capacitor (from Qin tw. Vss). The oscillator circuit is
supplied by the regulated voltage, Vreg. In SLEEP mode the oscillator is stopped.
With Fout bit in PA3cnt register we can put the system 32.768 Hz frequency on STB/RST pin as output.
4.1 Prescaler
The input to the prescaler is the system clock signal.
The prescaler consists of a fifteen (15) element divider
chain which delivers clock signals for the peripheral
circuits such as the timer/counter, buzzer, I/O
debouncers and edge detectors, as well as generating
prescaler interrupts.
The frequency of prescaler interrupts is software selectable, as shown in Table 6.
Table 7. Prescaler control register - PRESC
5
If for any reason the CPU crashes, then the watchdog timer can detect this situation and output a system reset
signal. This function can be used to detect program overrun. For normal operation the watchdog timer must be
reset periodically by software at least once every three seconds (CLK = 32kHz) or a system reset signal is
generated to CPU and periphery. The watchdog is active during STANDBY. The watchdog reset function can be
deactivated by setting the NoWD bit to 1 in the Option register.
In worst case because of prescaler reset function WD time-out can come down to 2 seconds.
The watchdog timer is reset by writing 1 to the WDRST bit. Writing 0 to WDRST has no effect.
The watchdog timer also operates in STANDBY mode. It is therefore necessary to reset it if this mode continues
for more than three seconds. One method of doing this is to use the prescaler 1Hz interrupt such, that the
watchdog is reset every second.
Table 8.Watchdog register - WD
Copyright  2002, EM Microelectronic-Marin SA
Oscillator
Watchdog timer
Bit
3
2
1
0
Bit
3
2
1
0
Name
MTim
PRST
PSF1
PSF0
Name
WDRST
Slmask
WD1
WD0
Reset
Reset
0
-
0
0
-
-
0
0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R
R
8
Table 6.Prescaler interrupt source
Interrupt frequency
mask(no interrupt)
1 Hz
8 Hz
32 Hz
Description
Timer/Counter Interrupt Mask
Prescaler reset
Prescaler Interrupt select 1
Prescaler Interrupt select 0
Description
Watchdog timer reset
SLEEP mask bit
WD Timer data 1/4 Hz
WD Timer data 1/2 Hz
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PSF1
0
0
1
1
EM6603
PSF0
0
1
0
1
03/02 REV. G/439