UPD17708 datasheet(202/356 Pages) NEC

202 / 356 page

202

µPD17704, 17705, 17707, 17708, 17709

15. D/A CONVERTER (PWM mode)

15.1 Outline of D/A Converter

Figure 15-1 outlines the D/A converter.

The D/A converter outputs a signal whose duty factor is varied by means of PWM (Pulse Width Modulation). By

connecting an external lowpass filter to the D/A converter, a digital signal can be converted into an analog signal.

Each pin of the D/A converter can output a variable-duty signal independently of the others.

Whether an 8-bit counter or 9-bit counter is used for the D/A converter can be specified by software.

When the 8-bit counter is selected, two output frequencies, 4.4 kHz and 440 Hz can be selected, and the duty factor

of the output signal can be varied in 256 steps.

When the 9-bit counter is selected, two output frequencies, 2.2 kHz and 220 Hz, can be selected, and the duty

factor can be varied in 512 steps.

When the D/A converter is not used, it can be used as timer 3, which counts the basic clock (1.125 or 0.1125 MHz)

with an 8-bit counter.

For the details of timer 3, refer to 13. TIMER 3.

Figure 15-1. Outline of D/A Converter

Remarks 1.

PWM2SEL through PWM0SEL (bits 2 through 0 of PWM/general-purpose port pin function selection

PWMBIT (bit 2 of PWM clock selection register: refer to Figure 15-2) selects the number of bits (8

or 9 bits) of the PWM counter.

PWMCK (bit 0 of PWM clock selection register: refer to Figure 15-2) selects the output frequency

of PWM timer.

TM3SEL (bit 3 of timer 3 control register: refer to Figure 15-5) selects timer 3 or D/A converter.

TM3RES (bit 0 of timer 3 control register: refer to Figure 15-5) controls resetting of timer 3 counter.

P1B0/PWM0

P1B1/PWM1

P1B2/PWM2

PWM0SEL flag

DBF

Multiplexed with timer 3

Duty setting block

TM3SEL flag

TM3RES flag

RES

fPWM

IRQTM3

Comparator

PWMBIT

PWMCK

Clock generation

block

9-bit or

8-bit counter

PWM data register 0

(PWMR0)

PWM data register 1

(PWMR1)

PWM data register 2

(PWMR2)

Output selection block

PWM1SEL flag

PWM2SEL flag

UPD17708 Datasheet(PDF) 202 Page - NEC

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