Hitachi MB-6890, Service Manual

Page: 54 / 123

6-4-4 Display character
modeChBHQ9 circuit
The display character mode switching
circuit (fig. 6-8, IC38)
is the circuit
to change
display mode
to
40 characters
or
80
characters.
Un
the
input side,
DOTCK, LOAD, CHRCK
and
GRENBLE
of 40 and
80 characters
use are
inputted. Each
signal of 40 characters mode,
when
IC38
l Pin input (SELECT terminal)
is
Low
level, and of 80 character
mode
when High Level,
are
outputted to IC38
output
pins lY-4Y.
6-4-5
CRTC
Block
CRTC block
generates
the signals for video signal
generators
and_supp1y
the
address
signal
for the
display to
the
RAM. Also,
have the function
to
recognise the location of the
light
pen on
the
screen.
The circuit
of CRTC
block is
written
in fig. 6-lO.
CRTC-SEL signal is
inputted to
EE
terminal
(25 pin)
of
came
(11:36)
and ABQ
signal to RS
terminal
(24 Pin)
to
select the register of
CRTC.E TTL signal
for the
system
clock is
inputted
to E
terminal and
CHRCK
signal for the clock
signal of
display address signal
to
the
CLK
terminal.
Data bus
is
connected
with
MPU data bus.
Fig.5-8
CRTC
Internal
Register Structure
Address Name of the
6?
RS
RSglSt@r
R e l § ? i S t
§egiSter
READ WRITE
4 3 2
1 o
g
1 x
xxxxx]
on
Valid
|
- -
o
o{xxxxx
AR
egfgigglt X
9
o 1
o o o o o
R0 Egrfifcghgiacte
X
O_
o 1 o o o
o 1 R1
. 8 ‹ § f t a |
><
O
o
1
1 o 0 0
1 0 R2
9E&H?B1t\67;!1S
Po
.X
O
us
pu se
O
o 1 o
o o 1 1
R3
1 1
_
1
_
1
_._. _
1
...
ertica1,tOta
X
I
n
I
,Q
|0’l{UU1uu|
M
a I a C t ‹ r l ’ 1 O . ] } ‘ - |
o 1
o o 1 o 1
R5
_A
] § $ t § 1 2 § § ? r
g
><
O
o 1 o
o 1 1 111
R6
Ea
ØgØØfdlllggl
YX
O
1o0111R7yncrji-onougkpo.><O 1
o 01 1 1
R7
yncrji-onougkpo
.><
O
o 1
o 1 o o o
R8
e ace ew
><
O
1
R
to ’
.
5’
t
o 1 o 1 o
o 1 R9
a § § r e S § - f s
er
><
O
o 1 o 1 o 1 o
R10
QBEQSE
Start
><
O
1
0101011
R11
ggggg§@H<
O
o 1 o 1 1 o
o R12
§ 1 § § " f t
adifessm
O O
o 1 o 1
1 o 1
R13
5(E?rt55addfeSS
O
O
o 1
y
o 1
1 1 o R14 cursor
g(H)
O O
‘o
1 o 1
1 1 1
R15
C f S f
(L)
O
O
’o
1 1 o o
o o
R16 light
pen
O ><
0,1 1
o o o 1
‘
R11
light
Pen O ><