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, _ _ LEAR SIEGLER, INC.
DATA PRODUCTS DIVISION
1.3.1 Keyboard
The keyboard contains 59 keys from which data
entry and control functions are initiated. Each
keystroke is encoded into a corresponding ASCII
character which is immediately transmitted to the
host computer. The character is also routed back
to the CRT display: directly in half-duplex
operation, or echoed from the host computer via
the input/output (I/O) interface in full-duplex
operation.
1.3.2 Input/Output (I/O) Port
The modem I/O portis the link, or interface, that
handles the flow of data in both directions
between the ADM 3A and the computer. It may be
configured for either RS-232C or optional 20mA
current loop operation.
With the modenl DTR or X-On/X-Off handshake
feature, all data transmitted from the host, even at
speeds up to 19,200 baud, will be received by the
ADM 3A without data loss (9600 for current loop.)
1.3.3 ADM 3A Control Logic
The ADM 3A control logic interprets the control
codes that originate either at the keyboard or host
computer, and directs the activities of the ADM
3A accordingly. These activities include data
handling and formatting.
1.3.4 Set-Up Mode
The ADM 3A features a non-volatile set-up mode
which allows the terminal parameters to be
selected through commands from the keyboard.
These parameters, including baud rates, word
structures, cursor type, communications control,
and operating modes, can then be "saved" in
memlory and retained when power is shut off.
1.3.5 Send/Receive Modes
Two selectable send/receive modes are available
in the ADM 3A through the set-up mode: half-
duplex and full-duplex. In the half-duplex mode,
each character is transmitted to the computer as it
is entered on the keyboard and is simultaneously
displayed on the CRT monitor.
In full-duplex operation, the ADM 3A can
transmit
and
receive
information in
both
directions simultaneously. Characters are
transmitted as they are entered at the keyboard,
1-3
but are displayed only upon reception. In order to
display transmitted characters, they must be
echoed back from the host computer or data set.
1.3.6 Display Memory
The display memory contains a random access
memory (RAM), video logic and character
generation circuits appropriate for controlling the
CRT display. The memory is capable of holding
1,920 characters, which are stored in sequentially
scanned locations. The scanned data is then sent
to the CRT for displaying. Input to the display
memory consists of the data character codes from
the I 0 port or keyboard, under the control of
signals from the control logic circuits.
1.3.7 CRT Display Monitor
The CRT display monitor is a rectangular screen
measuring 12 inches diagonally. Data characters
are displayed on 24 equally spaced rows, each
consisting of 80 characters. The 80-character lines
are displayed clearly at a refresh rate of either 50
or 60 Hz, corresponding to the AC line frequency.
1.4 PHYSICAL DESCRIPTION
The ADM 3A is a self-contained unit consisting of
four major assemblies:
(1)
base and cover
assembly, (2) main logic board,
(~-))
keyboard and
(4) the CRT monitor. The power transformer and
intercomponent cabling are located on the base
portion of the terminal.
The cover portion of the terminal contains the
CRT monitor and its associated subassemblies.
The cover is hinged to the base at the rear, and
when swung open, all components of the ADM 3A
are exposed.
The main logic board contains all other operating
elements of the ADM 3A that are not contained in
the CRT monitor, keyboard and the base
assembly. The logic board is connected to a metal
plate which anchors to the base supports of the
unit. Two connectors on the logic board provide
the RS-232C current loop interface and the RS-
232C extension interface.
The keyboard assembly is made up of integrated
key rows (or modules). It is connected to the main
logic board by an eight pin connector.
The CRT monitor consists of three subassemblies:
(1) the CRT itself, (2) a printed circuit board that
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