EF9345 Datasheet, PDF (29/38 Pages) STMicroelectronics – HMOS2 SINGLE CHIP SEMI-GRAPHIC DISPLAY PROCESSOR

EF9345
80 CHAR/ROW CHARACTER CODES
To display pages in 80 character per row format,
one of two character code formats must be se-
lected :
- Long (12 bits) code : 4 parallel attributes and large
on-chip 1024 semigraphic character set,
- Short (8 bits) code : no attribute, no semigraphic
set.
Both formats address the on-chip G0 set (128
characters 6 x 10). None allows UDS addressing.
Long Codes
Each 6 pixels x 10 lines character window on the
screen is associated with a 12-bit code in memory,
namely a C byte and an attribute nibble A (Fig-
ure 18). C7 bit designates the set.
- Alphanumeric set : C7 = 0
C(0:6) designates one out of 128 alphanumeric
characters in the G0 on-chip set. This set is
common to the 40 char/row format, with the 2 right
most columns truncated (see Figure 34).
A(0:3) gives 4 parallel attributes.
- Mosaïc set : C7 = 1
A(1:3) and C(0:6) address a dedicated mosaïc
character. Each of these address bits controls the
foreground/background status of a 3 pixels x 2
lines sub-window : foreground when the bit is set.
A0 provides a color select attribute.
Figure 28 : 80 Char/Row Character Code
76543210
0XXXXXXX
3210
NFUD
Short Codes
They are derived from the long code by giving a 0
implicit value to each bit of the A nibble : positive,
not underlined, not flashing.
Packing the Codes in Memory
Long codes are paired. A pair is packed in a 3-byte
word. Therefore, the 80 codes of a row fill a 120-
byte row buffer (Figure 29). The left most position
on the screen is even. Its corresponding C byte is
at the beginningof the first buffer. The next position
on the screen is odd. Its corresponding C byte is at
the beginning of the second buffer. Both nibbles
are packed in the third buffer. With short codes, the
same scheme yields 80-byte row buffers.
Access to the Codes in Memory
KRL command transfers 12 bits from/to the R1 and
R3 registers to/from memory. The read modify
write operation, necessary to write the A nibble in
memory, is automatically performed provided that
the A nibble is repeated in the R3 register (Fig-
ure 30). Dedicated auto-incrementationis also per-
formed when required.
KRC command does a similar job for the short
codes (Figure 31).
A very simple scheme allows the microprocessor
to transcode an horizontal screen location into a
pointer (Figure 32). The joint use of this scheme
with the dedicated command alleviates all the
packing/unpacking troubles.
76543210
1 XXXXXXX
3210
XXXD
C
ALPHANUMERIC CHAR CODE
N = Negative
F = Flash
U = Underline
D = Color set
128 ALPHANUMERICS
In G₀ set.
A
C
A
MOSAIC CHAR CODE
3 pels 3 pels
0
1
C0
2
3
C2
4
5
C4
6
7
C6
8 _A2
9
C1
C3
C5
DEDICATED
MOSAIC SET
A1
A3
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