P83C266BDR datasheet(61/92 Pages) PHILIPS

61 / 92 page

1999 Mar 10

Philips Semiconductors

Product speciﬁcation

Microcontrollers for PAL/SECAM TV

with OSD and VST

P8xCx66 family

17.6

Loading character data into display RAM

Three registers are used to address and load data into the

display RAM: OSAD, OSDT and OSAT. These registers

are described in Sections 17.6.1 to 17.6.3.

17.6.1

OSD ADDRESS REGISTER (OSAD)

This register holds the address of the location in display

RAM, into which character data is to be written.

Table 73 OSD Address Register (address 9BH)

17.6.2

OSD DATA REGISTER (OSDT)

This register holds the character font data that will be

loaded into bits <11-5> of the location in RAM addressed

by the contents of OSAD.

Table 74 OSD Data Register (address 9AH)

17.6.3

OSD ATTRIBUTE REGISTER (OSAT)

This register is loaded with character attribute data.

The data will be loaded into bits <4-0> of the location in

RAM addressed by the contents of OSAD. The actual

attribute is dependent upon whether the Character Font

Code, Carriage Return Code, Space Code 1 or Space

Code 2 has been selected.; this is explained in

Section 17.5.1. Bits 7 to 5 are not used and are reserved.

Table 75 OSD Attribute Register (address 99H)

76543210

AD7

AD6

AD5

AD4

AD3

AD2

AD1

AD0

76543210

−

76543210

−−

T4T3T2

−

17.7

Writing character data into the display RAM

The procedure for writing character data into the display

RAM is as follows:

1. Initialize the starting address of the display RAM by

writing data into OSAD.

2. Write the character attributes to OSAT. If the attributes

of a series of displayed characters are the same, the

contents of this register need not be changed; only

OSDT need be updated.

3. Write the character font code to be displayed to OSDT.

When the write to OSDT operation is finished an

automatic transfer occurs that loads the data stored in

OSAT and OSDT into the display RAM location

addressed by OSAD. The address held in OSAD is

then incremented by ‘1’.

4. Post increment operation is executed in OSAD

(OSAD

← OSAD + 1) making it point to the next RAM

location. On overflow OSAD is cleared. Figure 39

shows the post-increment operation.

Fig.39 OSAD post-increment operation.

handbook, halfpage

MGL282

189

190

191

OSAD

numbers are in decimal

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