7512 datasheet(39/87 Pages) RENESAS

39 / 87 page

Feb 18, 2005

page 39 of 85

REJ03B0122-0101

7512 Group

PULSE WIDTH MODULATION (PWM)

The 7512 Group has a PWM function with an 8-bit resolution,

based on a signal that is the clock input XIN or that clock input di-

vided by 2.

Data Setting

The PWM output pin also functions as port P44 or port P07. The

PWM output pin can be selected to either port P44/PWM0 or port

P07/PWM1 by bit 2 (PWM output pin selectoin bit) of the PWM

control register. Set the PWM period 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)

= 63.75 ✕ (n+1)

µs

(when f(XIN) = 4 MHz)

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

= 0.25 ✕ (n+1) ✕ m

µs

(when f(XIN) = 4 MHz)

Fig. 40 Timing of PWM period

Fig. 41 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.

63.75 ✕ m ✕ (n+1)

255

T = [63.75 ✕ (n+1)]

PWM output

m: Contents of PWM register

n : Contents of PWM prescaler

T : PWM period (when f(XIN) = 4 MHz

µs

PWM

prescaler pre-latch

PWM

Transfer control circuit

PWM

prescaler latch

PWM prescaler

PWM register

1/2

XIN

PWM enable bit

PWM register latch

Data bus

"1"

"0"

Count source

selection bit

Port P44 latch

PortP44/PWM0

PortP07/PWM1

PWM output pin selection bit

Port P07 latch

7512 Datasheet(PDF) 39 Page - Renesas Technology Corp

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