EF9345 Datasheet, PDF (16/38 Pages) STMicroelectronics – HMOS2 SINGLE CHIP SEMI-GRAPHIC DISPLAY PROCESSOR

EF9345
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).
Figure 13 : 40 Char/Row Fixed Long Codes
Bichrome Code
76543210
C BYTE
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).
Quadrichrome Code
76543210
LmH i
B BYTE
Insert
Double height
Conceal
Double width
Type and set
N B₁ G₁ R₁ F B₀ G₀ R₀
A BYTE
11
kR i
4 COLOR PALETTE
Insert
Low resolution
Subset index
(low resolution only)
Set number
16/38
Background color C₀
Flash (blink)
Foreground color C₁
Negative (reverse video)