ST72589BW datasheet(67/158 Pages) STMICROELECTRONICS

67 / 158 page

ST72589BW, ST72389BW

67/158

7.4 PWM/BRM GENERATOR (DAC)

7.4.1 Introduction

This PWM/BRM peripheral includes a 6-bit Pulse

Width Modulator (PWM) and a 4-bit Binary Rate

Multiplier (BRM) Generator. It allows the digital to

analog conversion (DAC) when used with external

filtering.

Note: The number of PWM and BRM channels

available depends on the device. Refer to the de-

vice pin description and register map.

7.4.2 Main Features

Fixed frequency: fCPU/64

Resolution: T

CPU

Steps of V

DD/2

10 (5mV if V

DD=5V)

7.4.3 Functional Description

The 10 bits of the 10-bit PWM/BRM are distributed

as 6 PWM bits and 4 BRM bits. The generator con-

sists of a 10-bit counter (common for all channels),

a comparator and the PWM/BRM generation logic.

PWM Generation

The counter increments continuously, clocked at

internal CPU clock. Whenever the 6 least signifi-

cant bits of the counter (defined as the PWM coun-

ter) overflow, the output level for all active chan-

nels is set.

The state of the PWM counter is continuously

compared to the PWM binary weight for each

channel, as defined in the relevant PWM register,

and when a match occurs the output level for that

channel is reset.

This Pulse Width modulated signal must be fil-

tered, using an external RC network placed as

close as possible to the associated pin. This pro-

vides an analog voltage proportional to the aver-

age charge passed to the external capacitor. Thus

for a higher mark/space ratio (high time much

greater than low time) the average output voltage

is higher. The external components of the RC net-

work should be selected for the filtering level re-

quired for control of the system variable.

Each output may individually have its polarity in-

verted by software, and can also be used as a log-

ical output.

Figure 41. PWM Generation

COUNTER

COMPARE

VALUE

OVERFLOW

000

PWM OUTPUT

CPU x 64

ST72589BW 数据表(PDF) 67 Page - STMicroelectronics

ST72589BW 数据表(HTML) 67 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载