Radio Shack TRS-80 Service Manual page 56

SIGNAL
NAME
(DATA STROBE)
DATA
1
DATA
2
DATA
3
DATA
4
DATA
5
DATA
6
DATA
7
DATA
8
ACKNLG
BUSY
PE
SLCT
±0V
OSCXT
±OV
STANDARD
INTERFACE SIGNALS
INTERFACE
CONNECTOR
CHASSIS
GROUND
+5V
INPUT PRIME)
FAULT
LINE
COUNT
PULSE
1.
19
2,20
3,21
4,22
5,23
6,24
7,25
8,26
9.27
10,28
11,29
12
13
14
15
16
17
18
31,30
32
34.35
SOURCE
DESCRIPTION
INPUT DEVICE A
1.0
/zsec pulse (min.) used
to clock data
from
the
pro-
cessor to the
printer
logic.
INPUT DEVICE
Input data
levels.
A
high represents
a
binary
ONE,
a
low
re-
INPUT DEVICE
presents
a
ZERO.
All printable characters
(i.e.,
codes having
INPUT DEVICE
a
ONE
in
DATA
6
or
DATA
7)
are stored
in
the
printer
INPUT DEVICE
buffer. Control
characters
(i.e.,
codes having
a
ZERO
in
INPUT DEVICE
both
DATA
6 and
DATA
7)
are used to specify
special
INPUT DEVICE
control functions.
These codes
are
not stored
in
the buffer
INPUT DEVICE
except when
they
specify
a
print
command
and
are pre-
INPUT DEVICE
ceded by
at least
one
printable character
in
that
line.
PRINTER
Acknowledge
pulse indicates the input of
a
character
into
memory
or the
end
of
a
functional operation.
PRINTER
A
level indicating that the printer
cannot
receive data.
For
conditions causing BUSY,
refer to
Busy
Condition Timing
Table.
PRINTER
A
level
indicating that
the
printer
is
out
of paper.
PRINTER
A
level
indicating that
the printer
is
selected.
PRINTER
Signal ground (Formerly
SS
signal,
older
version)
PRINTER
A
100
KHz
signal
(Modes
101,
101A, 102A,
101S) or 100-
200
KHz
signal (All other models).
Signal
ground
PRINTER
Frame
ground
PRINTER
+5
Volt power
bus
INPUT DEVICE A
level
which
clears the printer buffer and
initializes
the
logic.
(Not
in
101).
PRINTER A
level that indicates
a
printer fault
condition such
as
paper
empty,
light detect, or
a
deselect condition. (Not
in 101).
Both
sides
of the
line
count
switch appear
at
the
interface
connector. This switch
is
opened and
closed during each
line feed operation.
A
level delivered to the switch would
be pulsed
off
and on
each time
a line
feed operation
is
per-
formed.
(Series
300
and 500
except 306SC,
503).
NOT
USED
36
NOTE:
1.
Second
pin
number
indicates twisted
pair return (±OV).
A-2