PCE84C486 datasheet(13/36 Pages) PHILIPS

13 / 36 page

1996 Feb 21

Philips Semiconductors

Objective speciﬁcation

Microcontrollers for digital auto-sync and

VST TV controller applications

PCE84C486; PCE84C487

7.3

14-bit PWM output (PWM8)

The 14-bit PWM output can be used to generate the

Automatic Frequency Control (AFC) signal used in VST

applications.

PWM8 shares the same pin as Derivative Port line DP13.

Selection of the pin function as either a PWM output or as

a Derivative Port line is achieved using the PWM8E bit in

The Block diagram for the 14-bit PWM output is shown in

Fig.10 and comprises:

• Two 7-bit latches: PWM8L (Register 18) and PWM8H

(Register 19)

• 14-bit data latch (PWMREG)

• 14-bit counter

• Coarse pulse controller

• Fine pulse controller

• Mixer.

Data is loaded into the 14-bit data latch (PWMREG) from

the two 7-bit data latches (PWM8H and PWM8L) when

PWM8L is written to. The contents of PWMREG determine

the active time of the PWM8 output. The upper seven bits

of PWMREG are used by the coarse pulse controller and

determine the coarse pulse width; the lower seven bits are

used by the fine pulse controller and determine in which

subperiods fine pulses will be added. The outputs OUT1

and OUT2 of the coarse and fine pulse controllers are

‘ORED’ in the mixer to give the PWM8 output. The polarity

of the PWM8 output is programmable and is selected by

the P8LVL bit in Register 23.

As the 14-bit counter is clocked by 1

⁄3 × fxtal, the repetition

times of the coarse and fine pulse controllers may be

calculated as shown below.

Coarse controller repetition time:

Fine controller repetition time:

Figure 11 shows typical PWM8 outputs, with coarse

adjustment only, for different values held in PWM8H. Note

that the PWM8 coarse controller output is the same as the

7-bit PWM outputs except the polarity is reversed.

Figure 12 shows typical PWM8 outputs, with coarse and

fine adjustment, after the coarse and fine pulse controller

outputs have been ‘ORED’ by the mixer.

sub

384

xtal

----------

49152

xtal

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

7.3.1

COARSE ADJUSTMENT

An active HIGH pulse is generated in every subperiod; the

pulse width being determined by the contents of PWM8H.

The coarse output (OUT1) is LOW at the start of each

subperiod and will remain LOW until the time

has elapsed. The output will

then go HIGH and remain HIGH until the start of the next

subperiod. The coarse pulse width may be calculated as

shown below.

7.3.2

FINE ADJUSTMENT

Fine adjustment is achieved by generating an additional

pulse in specific subperiods. The pulse is added at the

start of the selected subperiod and has a pulse width of

3/fxtal. The contents of PWM8L determine in which

subperiods a fine pulse will be added. It is the logic 0 state

of the value held in PWM8L that actually selects the

subperiods. When more than one bit is a logic 0 then the

subperiods selected will be a combination of those

subperiods specified in Table 3. For example, if

PWM8L = 111 1010 then this is a combination of:

• PWM8L = 111 1110: subperiod 64 and

• PWM8L = 111 1011: subperiods 16, 48, 80 and 112.

Pulses will be added in subperiods 16, 48, 64, 80 and 112.

This example is illustrated in Fig.13.

When PWM8L holds 111 1111 fine adjustment is inhibited

and the PWM8 output is determined only by the contents

of PWM8H.

Table 3

Additional pulse distribution

PWM8L

ADDITIONAL PULSE IN SUBPERIOD

111 1110

111 1101

32 and 96

111 1011

16, 48, 80 and 112

111 0111

8, 24, 40, 56, 72, 88, 104 and 120

110 1111

4, 12, 20, 28, 36, 44, 52...116 and 124

101 1111

2, 6, 10, 14, 18, 22, 26, 30...122 and 126

011 1111

1, 3, 5, 7, 9, 11, 13, 15, 17...125 and 127

xtal

⁄

PWM8H

()

[]

Pulse duration

127

PWM8H

–

()

xtal

--------

PCE84C486 датащи(PDF) 13 Page - NXP Semiconductors

PCE84C486 датащи(HTML) 13 Page - NXP Semiconductors

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

датащи скачать

ссылки URL