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4.3
DETAILED FUNCTIONAL DESCRIPTION
A detailed discussion of the BEE HIVE B100 termi
nal operation is contained in the following para
graphs. The Subassembly components of the termi
nal are functionally interdependent, however, the
isolation of various functions to the responsible
subassembly is relatively simple. The function of
each subassembly is also described. Schematic
diagrams are provided in Section VI of this manual.
4.3.1
Power Supply
The Power Supply provides +5, +15, +12, and -12
VDC voltages to the circuitry from a 115 or 230
VAC source at 50 or 60 Hz. Figure 4-4 is a block
diagram of the Power Supply subassembly. The
DC regulators utilized are overcurrent and ther
mally protected.
The power applied to the Power Supply is step
ped down in voltage. The transformer output
voltages are rectified by three bridge circuits.
The output from the rectifiers and filters pro
vides power to the +5, +15, +12, and -12 VDC
regulator circuits.
4.3.2
Monitor
The monitor displays data on the CRT in a pattern
determined by the vertical and horizontal syn
chronization signals, and the video information
driving signals. A +15 VDC voltage is applied by
the Power supply to the Monitor. Appendix A
presents general and detailed data on the Moni
tor Assembly.
a3.3
Vertical Synchronization
Vertical synchronization is applied to the verti
cal oscillator and triggers it at the vertical re
fresh rate deternmned by the driving logic. The
vertical frequency is stabilized by the vertical
frequency control, which determines the point
of oscillation. The output pulse of the vertical
oscillator is applied to the driver amplifier
which shapes the pulse and is controlled by the
vertical linearity control. The output of the
driver amplifier is applied to the vertical
driver by way of the height control. The verti
cal driver output pulse is applied to the yoke
of the CRT and causes vertical deflection. The
refresh rate is 50 - 60 Hz. switch selectable.
4-6
4.3.4
Horizontal Synchronization
The horizontal synchronization pulses are applied
to the horizontal amplifier where they are ampli
fied and applied to the horizontal driver. The out
put of the horizontal drive is applied through the
width coil to the yoke, where it causes the horizon
tal deflection. The horizontal deflection signal is
also applied to the flyback transformer. The hori
zontal deflection signal is stepped up to approxi
mately 12 KV where it is then rectified, filtered
and applied to the anode cap of the CRT to pro
vide the high voltage required.
4.3.5
Video Information
The Video Information is applied to the video amp
lifier 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 corresponding
to light patterns of the screen. The brightness con
trol is external to the monitor and varies the vol
tage on the accelerating grid of the CRT.
4.3.6
Keyboard
The keyboard is compatible with ANSI standards.
Figure 3.2 defines the ASCII codes available.
Figure 1.2 shows the keyboard layout.
The keyboard enables the operator to manually
input information to the terminal. When a key is
depressed, the keyboard logic generates the corres
ponding 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 held there as long as the key
is held down. 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 func
tion line that is driven low for approximately 400
milliseconds when the key is depressed.The follow
ing keys cause special 8-bit (non-ASCII) codes:
AUXSEND, 1
t , CLEAR/HOME,SEND,
EOS, EOL, and DELETE CHAR. These codes are
used iplecnal to the CRT only and are not transmitted.
4.3.7
Display Organization
The main timing chain (oscillator, dot position
counter, character position counter, character
height counter, and character line counter)
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