EF9345 datasheet(16/38 Pages) STMICROELECTRONICS

16 / 38 page

40 CHAR/ROW CHARACTER CODES

To display pages in 40 character per row format,

one out of three character code formats must be

selected :

- Fixed long (24 bits) code : all parallel attributes.

- Fixed short (16 bits) code : mix of parallel and

latched attributes.

- Variable (8/24 bits) code : all latched attributes.

Fixed short and variable codes are translated into

fixed long codes by EF9345 during the internal row

buffer loading process. The choice of the character

code format is obviously a display flexibility/mem-

ory size trade off, left up to the user.

Fixed Long Codes

This is the basic 40 char./row code. Each 8 pixels

x 10 lines character window, on the screen is

associated with a 3-byte code in memory, namely

the C, B and A bytes (Figure 13). A row on the

screen is associated with a 120 byte row buffer in

memory.

3-BYTE Code Structure

1. C7 is a don’t care. Up to 128 characters may

be addressed in each set. Each user definable

set holds only 100 characters : C byte value

ranges from 00 to 03 and 20 to 7F (hexa).

2. B(4:7) give the type and set number of the

character.

3. All the bichrome characters have the same

attributes except that alphanumerics may be

underlined, semi-graphics cannot. Accentuated

alphanumerics allow orthogonal accentuating

of any one of the 32 lower case ROM characters

with any of 8 accents (see Figure 27).

4. Bichrome and quadrichrome characters use

two different coloring schemes.

For bichrome characters, character code byte A

defines a two color set by giving directly two color

values (Figure 14). The negative attribute ex-

changes the two values. Each bit of slice byte

selects one color value out of two.

The ”A” byte in a quadrichrome character code

defines an ordered 4 color set (Figure 15). When

more than 4 bits are set, higher ranking bits are

ignored. When less than 4 bits are set, the color set

is completed with implicit ”white” value. The slice

byte is shifted 2 bits at once at half the dot fre-

quency (

≈4MHz).

Each bit pair designates one color out of the 4 color

sets.

Quadrichrome characters allow displaying up to 4

different colors (instead of 2) in any 8 x 10 window

at the penalty of an halved horizontal resolution.

By programming the R attribute in byte B, one may

chose to keep the full vertical resolution (1 slice per

line) or to halve it (each slice is repeated twice). In

any case, it is possible to change the color set freely

from window to window and to mix freely all the

character types. So, fairly complex pictures may be

displayed at low memory cost.

Handling Long Codes

The KRF command allows an easy X, Y random

access or an X sequential access to/from the mi-

croprocessor from/to a memory row buffer (Fig-

ure 16).

6543

210

C BYTE

B BYTE

Insert

Double height

Conceal

Double width

Type and set

A BYTE

Background color C

Flash (blink)

Foreground color C

Negative (reverse video)

Bichrome Code

7654

3210

Insert

Low resolution

Subset index

(low resolution only)

Set number

4 COLOR PALETTE

Quadrichrome Code

Figure 13 : 40 Char/Row Fixed Long Codes

EF9345

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