Heathkit H9 Manual page 9

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BREAK
When this key is pushed in, it generates a continuous
space at the serial output, It is generally used to tell
the computer that you wish to interrupt execution. Do
not confuse this space with an ASCII space. It is de-
fined as zero current in a 20 mA current loop, an EIA
positive voltage, or a TTL logic 0. The BREAK key can
be pressed any time you want to terminate the trans-
mit page function.
FULL DUPLEX
When this key is released (out), the Terminal operates
in the half duplex mode. That is, data from the
keyboard or parallel input is written directly into
RAM and, at the same time, ASCII characters are sent
out the serial and parallel outputs. When the FULL
DUPLEX key is pushed in, the Terminal operates in
the full duplex mode. Data from the parallel input or
from the keyboard is sent to the computer and echoed
back to the Terminal before it is written into RAM and
displayed on the screen.
XMIT PAGE (Transmit Page)
When you momentarily press this key, data is trans-
mitted from the RAM (screen), starting from the cur-
rent cursor location and proceeding to the end of the
page. When it has completed the page, the cursor
returns home and the transmit page mode stops. The
data is transmitted simultaneously outboth the paral-
lel and serial ports at a rate determined by the slower
of the two ports. Press the BREAK key to interrupt the
transmit page function.
CTRL (Control)
When this key is used in conjunction with some of the
other keys, it changes those keys to special function
keys. For instance, CTRL M is equivalent to a return
(carriage return). The control key combinations are
shown in Pictorial 1-3.
SHIFT
When this key is used in conjunction with another
key, the character printed on the upper portion ofthat
key will be displayed. Since the Terminal does not
generate lower-case alphabetic characters, it is not
necessary to push the shift key to generate upper-case
alphabetic characters -
they are shifted automati-
cally in the keyboard encoder.
CTRL/SHIFT
These two keys are used in conjunction with other
keys to provide additional special function keys. For
instance, CTRL/SHIFT P (which means, press the
CTRL, the SHIFT, and the P keys at the same time)
puts an ASCII null fall zeros) on the bus.