Heathkit H9 - Active TTY Configuration

Page 18
TTY
(Active)
Connections
PICTORIAL
2.I2
I/O CIRCUIT
BOARD
Active
In
the active
configuration,
the 20 mA
loop
current is
supplied
by the Terminal,
usually
through
resistors
R629
or
R631.
Pictorial 2-1.2
shows the
jumper
wires
necessary
for
the TTY
(active)
configuration
on the
I/O
circuit board. A
mark is
defined
as
20
mA flowing
in
the
current loop.
A
space is defined
as less
than 4
mA flowing
in
the
current loop. Pictorial
2-13,
Page
19
shows the
partial
schematic
of the TTY
(active)
wiring.
The
jumper
wire
that disables
the reader
con-
trol is
shown in
Pictorials
2-1.2
and 2-t3. Refer
to
"Reader
Control"
on this Paee.
READER
CONTROL
The reader
control
circuit is
a serial handshake
that
allows
a
computer to
control
a
paper
tape reader
through
the Terminal
Serial I/O.
Normally,
the reader
control is
accomplished
by connecting
the tape
reader
to the
parallel
I/O
of
the
computer. If
this is not
possible,
and if
the computer
has a
spare serial
port,
the tape reader
can be
connected to
the Terminal
and
controlled
with
the reader
control
current loop. A
mark
in the loop
enables the reader;
a
space disables
the reader.
If your
systenr does
not require
this type
of reader
control
(and
most
won't)
,
the
circuit must
be disabled
by
connecting
a
jumper
wire from
the
base
[B)
of
transistor
Q604
to
ground (*J.
READFR
CONTROL
DISABLE