PCF8820 datasheet(27/60 Pages) PHILIPS

27 / 60 page

2000 Dec 07

Philips Semiconductors

Product speciﬁcation

× 101 Grey-scale/ECB colour dot matrix

LCD driver

PCF8820

handbook, full pagewidth

MGT128

VLCD

(V)

. . . 7D

value

LOW(1)

HIGH(2)

Fig.20 Generated VLCDOUT set by programming VLCD control register value (bits VOP6 to VOP0).

(1) Bit PRS = 0: VLCD programming range is LOW.

(2) Bit PRS = 1: VLCD programming range is HIGH.

The programming range for the generated VLCDOUT allows

values above the maximum value of VLCD. Therefore, the

user must ensure that the VLCD control register value and

the temperature coefficient selected, will never allow the

maximum VLCD limit to be exceeded for all conditions and

including all tolerances. The customer must also ensure

that the VLCD control register value will never be lower than

VDD1 or VDD2, except in the Power-down mode, for all

conditions and including all tolerances.

8.1.8

GREY-SCALE REGISTER AND GREY-SCALE LEVEL

The PCF8820 has 4 grey-scale registers selected by bits

GR0 and GR1, which define the four grey intensity levels.

Each of the 4 registers contain 6 bits allowing to select one

out of the 64 grey levels. A grey-scale register must be

addressed before it can be written to by using the

instruction ‘Grey-scale register’ (see Table 2). The content

of the grey-scale register (bits GS5 to GS0) is set by the

instruction ‘Grey-scale level control’ (see Table 2). It

should be noted that a grey-scale register setting of 63 is

internally converted to 64. Even numbers are preferred;

odd numbers produce a small DC component in the

waveform of the respective column (see Fig.3).

The grey-scale level for each pixel is effected by writing the

resultant grey-scale register value into the DDRAM (see

Fig.6).

One of the grey-scale registers can be used to create a

blinking cursor. The intensity of the pixels comprising the

cursor are to be defined by the value in the grey-scale

changed by selecting a different grey-scale register

containing a different grey-scale value.

A blinking cursor can be effected by continuously

switching the content of one grey-scale register between

the two grey-scales from e.g. white to black and back

again with a frequency of 2 Hz giving the impression of a

blinking cursor. This procedure causes less load for the

microcontroller than changing all pixels which form the

desired cursor. This implies the display has 3 grey-scale

levels left e.g. off, grey and on.

PCF8820 Datasheet(PDF) 27 Page - NXP Semiconductors

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