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PCE84C882

Microcontroller for monitor OSD and auto-sync applications

Philips Electronics 

Philips Semiconductors

Microcontroller for monitor OSD

and auto-sync applications

Preliminary specification

PCE84C882

7.2 14-bit PWM output

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

Register 22 (see Section 12.1).

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

Fig.7 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

either of these data latches is written to. 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, this is described

in Section 12.2.

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: tsub = 3-f-x--8-t--a4--l

Fine controller repetition time: tr = 4----9f--x-1-t--a5--l--2--

Figure 8 shows typical PWM8 outputs, with coarse

adjustment only, for different values held in PWM8H.

Figure 9 shows typical PWM8 outputs, with coarse and

fine adjustment, after the coarse and fine pulse controller

outputs have been ‘ORED’ by the mixer.

7.2.1 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

[3 ⁄ fxtal × (PWM8H + 1) ] 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.

Pulse duration = (127 – PWM8H) × -f-x-3--t-a--l

7.2.2 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.10.

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

111 1110

111 1101

111 1011

111 0111

110 1111

101 1111

011 1111

ADDITIONAL PULSE IN SUBPERIOD

64

32 and 96

16, 48, 80 and 112

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

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

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

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

1996 Jan 08

11

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