The system is composed of three types of hardware: display electronics
units; display units that include the CRTs; and keyboard units,
which together communicate with the GPCs over the display/keyboard
data bus network.
The MCDS provides almost immediate response to flight crew inquiries
through displays, graphs, trajectory plots and predictions about
flight progress. The crew controls the vehicle system operation
through the use of keyboards in conjunction with the display units.
The flight crew can alter the system configuration, change data
or instructions in GPC main memory, change memory configurations
corresponding to different mission phases, respond to error messages
and alarms, request special programs to perform specific tasks,
run through operational sequences for each mission phase and request
Three keyboards are located on the flight deck: two on the left
and right sides of the flight deck center console (panel C2) and
one on the flight deck at the side aft flight station (panel R12).
Each consists of 32 momentary double-contact push button keys.
Each key uses its double contacts to communicate on separate signal
paths to two DEUs. Only one set of contacts on the aft station
keys is actually wired because this keyboard can communicate with
only the aft display electronics unit.
There are 10 number keys, six letter keys (used for hexadecimal
inputs), two algebraic keys, a decimal key, and 13 special key
functions. Using these keys, the flight crew can ask the GPC more
than 1,000 questions about the mission and condition of the vehicle.
Each of the four DEUs responds to computer commands, transmits
data, executes its own software to process keyboard inputs and
sends signals to drive displays on the CRTs (or display units).
The four DEUs store display data, generate the GPC/keyboard unit
and GPC/display unit interface displays, update and refresh on-screen
data, check keyboard entry errors and echo entries to the CRT
There are three CRTs (or display units) on flight deck forward
display and control panel F7 and one at the side aft flight deck
station on panel R12. Each CRT is 5 by 7 inches.
The display unit uses a magnetic-deflected, electrostatic-focused
CRT. When supplied with deflection signals and video input, the
CRT displays alphanumeric characters, graphic symbols and vectors
on a green-on-green phosphorous screen activated by a magnetically
controlled beam. Each CRT has a brightness control for ambient
light and flight crew adjustment.
The DEUs are connected to the display/keyboard data buses by
multiplexer interface adapters that function like those of the
GPCs. Inputs to the DEU are from a keyboard or a GPC. The CRT
switches on panel C2 designate which keyboard controls the forward
DEUs and CRT (or DUs). When the left CRT sel switch is positioned
to 1, the left keyboard controls the left CRT 1; if positioned
to 3, it controls the center CRT 3. When the right CRT sel switch
is positioned to 2 , the right keyboard controls the right CRT
2; if positioned to 3 , it controls the center CRT 3. If the left
CRT sel and right CRT sel switches are both positioned to 3, keystrokes
from both keyboards are interleaved. Thus, flight crew inputs
are made on the keyboards and data is output from the GPCs on
the CRT displays.
The aft station panel R12 keyboard is connected directly to the
aft panel R12 DEU and CRT (or DU); there is no select switch.
Each DEU/DU pair, usually referred to as a CRT, has an associated
power switch. The CRT 1 power , on , stby , off switch on panel
C2 positioned to stby or on allows control bus power to activate
RPCs and sends MNA power to DEU/ DU 1. The stby position warms
up the CRT filament. The on position provides high voltage to
the CRT. The CRT 2 switch on panel C2 functions the same as the
CRT 1 switch, except that CRT 2 is powered from MNB. The CRT 3
switch on panel C2 functions the same as the CRT 1 switch, except
that CRT 3 is powered from MNC. The CRT 4 switch on panel R12
functions the same as the CRT 1 switch, except that CRT 4 is powered
from MNC. The respective keyboards receive 5 volts of ac power
to illuminate the keys. Each DEU/DU pair uses about 300 watts
of power when on and about 230 watts in standby.
The CRT 1, 3, 2, major func, GNC, SM and PL switches on panel
C2 tell the GPCs which of the different functional software groups
is being processed by the keyboard units and what information
is presented on the CRT. The CRT 4 , major func, GNC, SM and PL
switches on panel R12 function in the same manner.
Positioning the display electronics unit 1, 2, 3, 4 switches on
panel O6 to load initiates a GPC request for data stored in mass
memory through a GPC before operations begin. The information is
sent from the mass memory to the GPC and then loaded from the GPC
into the DEU memory.
It is possible to do in-flight maintenance and exchange DU 4
with DU 1 or 2. DU 3 cannot be changed out because of the control
and display panel configuration. Also, either forward keyboard
can be replaced by the aft keyboard. The DEUs are located behind
panels in the middeck. DEUs 1 and 3 are on the left, and DEUs
2 and 4 are on the right. DEU 4 can replace any of the others;
however, if DEU 2 is to be replaced, only the cables are changed
because 2 and 4 are next to each other.
The DEUs and DUs are cooled by the cabin fan system. The keyboard
units are cooled by heat dissipation.