Keyboard; Logic Board - Beehive International B102 Service Manual

vertical driver output pulse is applied to the yoke
of the CRT and causes vertical deflection. The re
fresh rate is 50-60 Hz switch selectable.
Horizontal Synchronization pulses are applied to
the horizontal amplifier where they are amplified
and applied to the horizontal driver. The output
of the horizontal drive is applied through the width
coil to the yoke, where it causes the horizontal de
flection. The horizontal deflection signal Ts stepped
up to approximately 12 kv where it is then recti
fied, filtered and applied to the anode cap of the
CRT to provide the high voltage required.
Video Information is applied to the video ampli
fier by way of the contrast control, external to
the monitor. The video information signal from
the video amplifier is applied to the cathode of
the CRT gun to cause an ON/OFF condition cor
responding to light patterns of the screen. The
brightness control is external to the monitor and
varies the voltage on the accelerating grid of the
CRT.
4.2.3 Keyboard
The Keyboard is the input device used by the
operator to communicate with the terminal. The
Keyboard contains the switches and supporting
circuitry to generate the appropriate control sig
nals and ASCII codes utilized in the B100 Series
terminals. The Keyboard conforms to the pro
posed ANSI keyboard standard for data keys, but
has been expanded to facilitate the capabilities
of the B100 Series terminals. The ASCII code
chart is found in Section III of the Operator
Manual.
The Keyboard enables the operator to manually
input information to the terminal. When a key
is depressed, the keyboard logic generates the
corresponding 7-bit ASCII code and presents the
data in parallel form to the keyboard data lines.
After a short delay for debouncing, the strobe is
driven to its active level and returns after approxi
mately 30 milliseconds. For those keys which auto-
repeat, the strobe line is pulsed at a 15 character
per second rate. The BREAK key is not encoded
but is a function line that is driven low for approxi^
mately 400 ms when the key is depressed. The
following keys cause special 8-bit (non-ASCII)
4-5
codes: AUXSEND, CLEAR/HOM^ SEND,
EOS^ EOL, and DELETE CHAR. These codes are
used internal to the CRT only and are not trans
mitted.
424 Logic Board
The Logic Board contains the major function and
control circuits in the B100 Series terminal. It also
holds all of the DC voltage regulators to power the
unit with exception of the +5 V regulator. The
basic operations accomplished by the main logic
board are: Generation of data and control signals
for the monitor, interaction with the keyboard,
control of the data sent between the BlOO
terminals and any external device, and generation
of the basic timing signals essential for the oper
ation of the terminal. (See Figure 4-6)
Display Organization - B100/B102 —The main
timing chain (oscillator, dot position counter,
character position counter, character height
counter, and character line counter) defines the
configuration of the display on the CRT. There
are 30 lines, six of which are used for vertical
retrace and 24 of which are used to display char
acters. The 30 lines are composed of nine scans
each, each scan being composed of 96 character
positions, 80 for display and 16 for horizontal re-
traca Each character block is composed of 7 x 9
dot matrix field which contains a 5x 7 character
matrix for the displayed character (see Figure44).
Display Organization - B150/B152 —The main
timing chain (oscillator, dot position counter, char
acter position counter, character height counter,
and character line counter) defines the configuratior
of the display on the CRT. There are 27 lines, three
of which are used for vertical retrace and 24 of
which are used to display characters. The 27 lines
are composed of ten scans each, each scan being
composed of 7x 10dot matrix field which contains
a 5 X7 character matrix for the displayed char
acter (see Figure 4-5).
Oscillator - The oscillator is crystal controlled
with a frequency of 10.8864 MHz. Two 74H04'!
are connected in series by a lOOpf capacitor.