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EM78P809N
8-Bit Microcontroller
46 •
Product Specification (V1.0) 07.26.2005
(This specification is subject to change without further notice)
4.11.4 PWM Mode
In Pulse Width Modulation (PWM) Output mode, counting up is performed using the
internal clock. The contents of the TCR4 are compared with the contents of the
up-counter. The F/F is toggled when match is found. The counter is still counting, the
F/F is toggled again when the counter overflows, then the counter is cleared. The F/F
output is inverted and output to the /PWM pin. A TC4 interrupt is generated each time
an overflow occurs. TCR4 is configured as a 2-stage shift register and, during output,
will not switch until one output cycle is completed even if TCR4 is overwritten.
Therefore, the output can be changed continuously. TRC4 is also shifted the first time
by setting TC4S to “1” after data is loaded to TCR4.
01
n-1
n
n+1
FE FF
0
n+1
FE FF
0
Source Clock
Up-counter
TCR4
TC4 Interrupt
n/n
n+2
F/F
/PWM
Match
Overflow
n-1
n
Match
n+2
Overflow
1 Period
n/m m/m
Overwrite
Shift
m-1
1
m
Fig. 27.Timing Chart for PWM Mode
4.12 TCC/WDT & Prescaler
An 8-bit counter is available as prescaler for the TCC. The PSR0~PSR2 bits determine
the ratio. The prescaler is cleared each time the instruction is written to TCC under
TCC mode.
R1 (TCC) is an 8-bit timer/counter. The clock source of TCC is the internal clock. If the
TCC signal source is from the internal clock, TCC will increase by 1 at every instruction
cycle (without prescaler). CLK=Fosc/2 or CLK=Fosc/4 selection is determined by the
CODE Option bit CLK status. CLK=Fosc/2 is used if CLK bit is "0", and CLK=Fosc/4 is
used if CLK bit is "1".
The watchdog timer is a free running on-chip RC oscillator. During normal operation
mode, a WDT time-out (if enabled) will cause the device to reset or interrupt by setting
WDTO. The WDT can be enabled or disabled any time during normal mode by
software programming. Without prescaler, the WDT time-out period is approximately
18 ms (default). The WDT can also be used as a timer to generate an interrupt at fixed
interval.