DEC VT220 Technical Manual page 129

You can install the keycaps manually, but you need a special tool
to remove them.
The keyboard circuitry is contained in a low profile cabinet that
has a 30 mm nominal height from table top to home row. The
keyboard case is made of two plastic shells that you can separate
with a screwdriver. Nonslip plastic strips along the bottom
prevent the keyboard from sliding on a table top. You can manually
insert two feet in holes to raise the back edge of the keyboard.
You can lift a plastic window along the top edge above the special
function keys to insert a user function label. The label, a thin
paper' strip, fits into the indented space and varies according to
the application program.
A coiled cable (PN BCC01), with a 4-pin modular connector on each
end, connects the keyboard to the video monitor. The keyboard
transmits four signals to the monitor, which pass unchanged to the
system box via the video cable (Figure 7-3). The four signals are
as follows.
• +12 V power to keyboard
• Ground to keyboard
• Serial out (transmit line from keyboard)
• Serial in (receive line to keyboard)
You can place the cable in a channel in the bottom case and the
modular type telephone connector fits into jack J4. You can insert
the cable in the channel on either side of the keyboard. Section
7.6 provides keyboard specifications.
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Figure 7-3 Keyboard Cable Connections
7-3