Heathkit H9 Manual page 20

Page 18
TTY (Active) Connections
PICTORIAL 2.I2
I/ O C I R C U IT
B O A R D
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
CONTR OL
DISABLE