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, cou nting 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 fo und. 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 /PW M pin. A TC4 interrupt is generated each time
an overflow occurs. TCR4 is configured as a 2-stag e shift register and, during output,
will not switch until one output c ycle is completed even if TCR4 is overw ritten.
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 nn+1 FE FF 0n+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
1m
Fig. 27.Timing Chart for PWM Mode
4.12 TCC/WDT & Prescaler
An 8-bit counter is available as presca ler for the TCC. The PSR0~PSR2 bits dete rmine
the ratio. The prescaler is cleared e ach time the instruction is written to TCC under
TCC mode.
R1 (TCC) is an 8-bit timer/counter. The clo ck 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 inter rupt 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.