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D
I
A
G
R
A
MIIÄ
lem. which must
be
ihvestioated.
6.1
M1cRo-PRocEssoR coNTRoL UNIT
The
Facit
TWIST
terminal
is
based upon
the
Z80A
Microprocessor.
The
principal function is to
5.3
TRANSPARENCY MODE-
GROUP
C,
SWITCH
2;g
decode
each
character
as
it
is
received (from
the host
computer
or
from
the keyboard), detect
When
this
switch
is
set
to
0
(nofauit
va1ue=0),
characters
and
character
sequences
representing
the
terminal displayg only
normai
dispiayabie
terminal
commands, and
obey
these
commands. The
characters.
when
the
Switch
15
Set
to
1
any
microprocessor also performs
background
tasks
control
codes (Hex 00
to
1F
and
7F)
are
dis-
Of
keYb0äYd
$Cä""l"9,
Chêräcter land
cursor
played
on
the
screen
in
reverse video
as
a
*
bïlklg,
beïï 9@"efätï0",
10ädl"9 the
dïSDïäy
followed
by
the corresponding alpha
character,
"?ff@$h
RAM
Staftlng
äddP@SS
f0P
eäßh
of
the
e.g.
Control
A
(Hex
01)
15
di5p1ayed
as <*A>_
display
rows,
and
various other
real-time func-
The
Commands
are
not
oooyed,
So
that
the
term1_
tions.
The
microprocessor
controls
all
communi-
nal
displays
a
continuous
string of
intermixed
Catl°"
0"
the
CPU
ÜUS,
reading
äïï
data
from
control
oodog and
thapaCterS_
the
EPROMs,
the
EAROMs,
display refresh
RAM,
the
I/0
DART,
the
keyboard,
writing
to
the
display refresh
RAM, DART,
CTC, CRTC, EAROMs,
and
various
hardware
latches.
The
2k
x
8
5.4
CUSTOM
MODE
SET-UP
scratchpad
RAM
is part of
the
Screen
MAP
RAM.
Custom
Mode
Set-Up
4
contains
Some
very
System
A
block
diagram
of
the Microprocessor
control
dependent
functions
and
re-assignment
of func-
U"It
IS $h°W"
ln
FI9
5-1
tion
keys
and
editing
keys. This
may
cause
some
problem
for
the
service technican,
therefore,
check
this
set-up
mode
prior
to
any
trouble-
shooting.
P°'°t"ai
t
MEMORY
|
RAM
FIG
6.1
FuNcnoNAL
stock
DIAGRAM
L.
____ ____
_
SET-UP
MODE
EÅROM
(350x8)
CHARACTER GENERATOR ROMS
DISPLAY
-
SYNC
KEYBDARD
T
GEN
Interface
I/O
PORTS
scREEn«MAP
RAM
PROGRAM
.
ROM
DISPLAYED
VIDEO
RINTER
I/0
(40kX8)
CHARACTERS
ATTR
_
Interface
Interface
(8kx8)
(5kx8)
Z80A
Landscape/
CPU AND
|2kx8
INTERFACE
(2X4|<x3)
GENERA oR
VIDEO
Bell
and
keyklickerl
"I
SERIAL
ASCII
VIDEO
COMBINER
CIRCUIT
DISPLAY
KEYBDARD
LOGIC
AND
ENCODER
KEYBDARD
KEYBDARD
KEY
MATRIX
LEDS
/
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