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_ _ _ _ LEAR SIEGLER. INC.
OATA PRODUCTS DIVISION
1.3
OPERATIONAL DESCRIPTION
The ADM-3A is an interactive device which is used to enter, dis-
play, and send information to a host computer, and to receive
and display information from the computer.
Using a keyboard
similar to that of a teletypewriter an operator may enter infor-
mation which is immediately transmitted to the computer (and
may be simultaneously displayed on a CRT).
Data from the com-
puter is received and displayed at a rate as great as 1920 char-
acters per second.
Figure 1-2 illustrates the functional areas
of the ADM-3A and the overall flow of data through them.
1.3.1
Keyboard
Data to be processed
by
the terminal originates either at the
keyboard or with the host computer.
Keyboard entry is made
using one of the 59 keys on the keyboard.
Each key-stroke is
encoded into a parallel
ASCII
character which is immediately
transmitted to the host computer.
The character is also echoed
back to the CRT display:
directly, via the I/O Channel,
in
Half
Duplex operation; via the host computer and the I/O Channel, in
Full Duplex operation.
1.3.2
Input/Output (I/O) Channel
The I/O Channel is the link, or interface, which handles the
flow of data in both directions between the ADM-3A and the com-
puter.
In Half Duplex operation, the I/O Channel also routes
each character entered and. transmitted back to the Control Logic
and Display Memory for CRT display.
The I/O Channel includes
the baud rate selection logic and the RS-232C extension cir-
cuitry.
1.3.3
ADM-3A Control Logic
The
ADM-3A
Control Logic interprets all the control codes which
originate either at the keyboard or host computer, and directs
the activities of the ADM-3A accordingly.
These activities
include:
basic timing; data, handling and formatting; video and
status control; and I/O interfacing control.
1.3.4
Display Memory
The Display Memory contains the random access memory
(RAM),
video logic, and character generation circuits appropriate for
controlling the CRT display.
The memory is capable of holding
960 (optionally 1920) characters, which are stored in sequen-
tially scanned locations.
The scanned data is sent to the CRT
for display.
Input to the Display Memory consists of the data
character codes from the I/O Channel, under the control of Con-
trol Logic signals.
1-2
DPI04
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