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computer and a keyboard for presentation on a CRT
screen. Data is input to the processor in serial through
RS-232C standard ports. The keyboard although laid
out like a standard typewriter, contains additional keys
for communicating with a computer. Unlike a typewriter
(where pressing a key results directly in a typed
character), the Model 950 keyboard transmits a code
(American Standard Code for Information Interchange.
ASCII) to the display processor for action. Depending
on the terminal's communication mode, the processor
either sends the typed character directly to the screen or
transmits it to the host for action.
NOTE
What the host computer sends back to the
Model 950
(if
anything) depends entirely
on the application program in use. Refer
to your application program user docu-
mentation for complete information.
The Model 950 may be set to one of four transmission
modes. In the Local mode (see Figure 3-2), the display
processor sends keyboard entries directly to the screen
for presentation (characters) or for control. The Block
mode sends keyboard entries to the screen, and when the
operator chooses, it sends the entries as a block of text to
the host computer. The Half Duplex mode sends key-
board entries to the screen and to the host at the same
time. The Full Duplex mode sends keyboard entries to
the host only; if the host is programmed to act upon a
code received from a keyboard entry, it may send the
result back to the terminal. For example if the A is
pressed on the keyboard, the host will probably send the
character A back to the terminal's display processor for
writing on the screen.
The Model 950 displays data entered from the keyboard
or from a host computer into the terminal on an 80 col-
umn by 24 line screen (see Figure 3-3). A 25th line at the
bottom of the display presents terminal status and user
messages. Data entered into the terminal is organized in
pages of 24 lines (or optional 48-line or 96-line pages).
These pages may be flipped through with the line feed
function (using Auto Page) or a page selection control
sequence.
A printer with an RS-232C serial data port may be con-
nected to the Model 950 to print page data stored in
memory or to print data sent from the host.
The controls of the Model 950 consist of the keyboard
for normal operation (see Figure 3-4) and setup switches
at the rear panel for configuration (see Figure 2-5). The
keyboard consists of six functional areas: the alpha-nu-.
meric keys, the editing and cursor control keys (local or
duplex operation), the function keys (local or duplex
operation), the SET- UP/NO SCROLL key (a unique
function -local operation only), Local Escape and shift
Break (local operatiop only), the BREAK key (Full
Duplex only), and the key modifiers.
3.3.1 Alpha-Numeric Keys.
The alpha-numeric key group (see Figure 3-4) contains
all the "typewriter" letter, number, and symbol keys on
the keyboard. This group also contains the carriage
RETURN, LINEFEED, ENTER, LOC ESC/ESC, and
DEL keys. All alpha-numeric keys repeat when pressed
for more than Yz second.
The RETURN and ENTER keys perform the same func-
tion .. They send the ASCII code for a carriage return
(CR) to the display processor. Depending on the termin-
al's communication mode, the code causes the processor
to transmit a CR to the host and the cursor to be moved
to column 1 of the current line.
NOTE
The Model 950 features a wraparound
function, which eliminates the need to
manually enter a carriage return and a
line-feed at the end of each SO-character
line.
The LINEFEED key sends an ASCII code for a linefeed
(LF) to the display processor. Depending on the termin-
al's communication mode, the code causes the processor
to transmit an LF code to the host and/or the cursor to
be moved down one line on the screen.
The ESC key sends an ASCII code for Escape to the dis-
play processor. The key is generally used to momentarily
leave (escape) an application program in order to use a
special feature or function.
When pressed, ESC causes the next control character en-
tered to be displayed on the screen. For example, press-
ing ESC CTRL A causes SH to be displayed.
When pressed in combination with SHIFT, the key oper-
ates only locally to invoke the terminal's functions and
special features.
It
causes the next character entered to
be interpreted as a command. For example, pressing
SHIFT LOC ESC
<
turns keyclick off and pressing
SHIFT LOCK ESC> turns keyclick on.
The DEL key sends an ASCII DEL character to the dis-
play processor, and depending on the terminal's commu-
nication mode, the processor retransmits an ASCII DEL
code to the host.
~
- - - FROM KEYBOARD
~
-
- -
-
TOfFROM HOST
r-::l
D
I
L-----
1
------8
DISPLAY PROCESSOR
3-9
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