SZF2002 datasheet(23/76 Pages) PHILIPS

23 / 76 page

1998 Aug 26

Philips Semiconductors

Product speciﬁcation

Low voltage 8-bit microcontroller with

6-kbyte embedded RAM

SZF2002

13 PULSE WIDTH MODULATED OUTPUT

One Pulse Width Modulated output channel PWM is

provided which outputs pulses of programmable length

and interval. The repetition frequency is defined by an 8-bit

prescaler (PWMP) that generates the clock for the

counter. The 8-bit counter counts modulo 255, i.e. from

0 to 254 inclusive. The value held in the 8-bit counter is

compared to the contents of the register PWM. If a new

prescaler value is written in register PWMP the 8-bit

counter finishes uninterrupted, and the new prescaler

value is used in the next count cycle.

Provided the contents of this register are greater than the

counter value, the PWM output is set HIGH. If the contents

of register PWMP are equal to, or less than the counter

value, the PWM output is set LOW.

The pulse-width-ratio is therefore defined by the contents

of register PWM. The pulse-width-ratio will be in the range

0to 255

⁄255 and may be programmed in increments of 1⁄255.

The repetition frequency (fPWM) at the PWM output is given

by:

For fclk = 12 MHz, the above formula gives a repetition

frequency range of 92 Hz to 23.5 kHz.

By loading the PWM register with either 00H or FFH, the

PWM output can be retained at a constant LOW or HIGH

level respectively. When loading FFH into the PWM

value.

The PWM output pin is not shared with any other function.

PWM

clk

(

PWMP

) 255

-----------------------------------------------------------------

Fig.12 Functional diagram of Pulse Width Modulated output (PWM).

handbook, full pagewidth

MGM140

fclk

PWMP

DIVIDE-BY-2

8-BIT COUNTER

PWM

8-BIT COMPARATOR

OUTPUT

BUFFER

PWM

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