M38042F6HKP datasheet(53/116 Pages) RENESAS

53 / 116 page

Rev.1.01

Jan 25, 2005

page 53 of 114

REJ03B0131-0101Z

3804 Group (Spec. H)

PULSE WIDTH MODULATION (PWM)

The 3804 group (Spec. H) has PWM functions with an 8-bit reso-

lution, based on a signal that is the clock input XIN or that clock

input divided by 2 or the clock input XCIN or that clock input di-

vided by 2 in low-speed mode.

Data Setting

The PWM output pin also functions as port P56. Set the PWM pe-

riod by the PWM prescaler, and set the “H” term of output pulse by

the PWM register.

If the value in the PWM prescaler is n and the value in the PWM

PWM period = 255 ✕ (n+1) / f(XIN)

= 31.875 ✕ (n+1)

µs (when f(XIN) = 8 MHz)

Output pulse “H” term = PWM period ✕ m / 255

= 0.125 ✕ (n+1) ✕ m

µs

(when f(XIN) = 8 MHz)

Fig. 45 Timing of PWM period

Fig. 46 Block diagram of PWM function

PWM Operation

When bit 0 (PWM enable bit) of the PWM control register is set to

“1”, operation starts by initializing the PWM output circuit, and

pulses are output starting at an “H”.

If the PWM register or PWM prescaler is updated during PWM

output, the pulses will change in the cycle after the one in which

the change was made.

31.875 ✕ m ✕(n+1)

255

µs

T = [31.875 ✕ (n+1)]

µs

PWM output

m: Contents of PWM register

n : Contents of PWM prescaler

T : PWM period (when f(XIN) = 8 MHz

Data bus

Count source

selection bit

“0”

“1”

PWM

prescaler pre-latch

PWM

prescaler latch

PWM

Transfer control circuit

PWM register

1/2

XIN

XCIN

Port P56 latch

PWM enable bit

Port P56

PWM prescaler

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