ay cog aR ne ers ee a|
|
Low-Speed
| As many as
| Line Control | 30 Low-
|
| Speed Lines
J |
|
oe ek4
| -
| |
Data |
| ae Storage |
| trol :
Date 1. — |
| Regis-
Regis-
|
| ter ter |
|
Control |
| Storage ~ |
| ! |
| Input Output |
High-Speed
High-Speed
|
Line
Control
Line Control
|
|
7
]
|
i
id
y
Mod Demod Demod
y
j
Input Line
j
Full-Duplex
High-Speed
Output Line ead
Figure 18. Principal
Components of the Terminal
Interchange
data may,
in
some
mode,
pass
from
one section
to an-
other
within
the interchange.
The section
on “Modes
and Data
Flow”
discusses
which
direction
the
data
follow
in each
mode.
Storage
The storage
unit
comprises
39 buffers
(data
storage
)
and one
control
storage.
An
auxiliary
storage
houses
the remaining
control
information.
DATA
STORAGE
As many
as
39
messages
or message
segments
of up
to
98 data
characters
may
be stored
in the
buffers.
If a
message
coming
in
from
the
terminal
set exceeds
98
characters,
the interchange
automatically
assigns
the
20
next available
buffer
to continue
storing
the
message
and enters the
terminal address
and a segment
identi-
fier character into
the new buffer.
The “end-of-message-
complete” is entered
by the
agent’s set
at the end of
the last segment
of the
message.
If the agent pushes
the reset
button during
an input
message, the
storage area
for that
message
segment is
cleared. The computer,
by programming,
automatically
clears previous
segments.
As soon as a 100-character
buffer is filled,
or the end-
of-message character
is recognized, the
contents of the
buffer are ready
for transmission.
Any
additional in-
coming information
is assigned
to a
new buffer.
CONTROL
STORAGE
Each terminal interchange
contains storage
positions to
accommodate
enough control
words to
control the
input from,
and output
to, 30
terminals and
a full-
duplex high-speed
line. The
auxiliary storage
contains
one half of each
control word;
the remaining
halves
are stored in
the control section
of main
storage. The
terminal interchange
automatically
forms
a control
word for each
message
it processes.
The functions
of
the control
word (and
its location)
are to:
1. Assign a buffer
for each
message, input
and out-
put, and keep
an updated record
of the storage
position
of the character
being
processed.
2. Determine
the timing
to read in and
read out
bits at various
speeds. Included
in this
function are
delays after
the type-head
carrier
returns
(and tabu-
lates in special
request
systems)
sent to terminal
sets.
3. Queue as many
as 31 messages
to be transmitted
over the high-speed
line.
4. Identify whether
a message
is incoming
or out-
going.
5. Control an
output message
until the
terminal set
is ready
to accept
it.
6. Translate
the multiple-character
telegraph
end-
of-message into
the pcp end-of-message-complete
char-
acter, on direct
input
telegraph
messages.
7. Perform parity
check on
characters received
from
terminals.
The control word
for each
terminal and
high-speed
line is placed
in storage.
The control
word
is placed
temporarily in
the control register
during
bit process-
ing and is then
replaced
in storage.
The function
of the
control register
is to control
the input and
output to
and from high-speed
and low-speed
lines.
Operator’s
Panel
The terminal
interchange
is an
automatic,
normally
unattended
component
of 9000
series systems.
How-
ever, it has
an operator’s
panel
containing
two indi-
cators, two
switches,
and two
keys:
Power
On Indicator: This
light is on when electric
power is on in the terminal interchange.
System
Available Indicator:
This light is normally
on.
It signifies that the system is available.
Power
On-Off Switch: Turning
this switch to on
brings
115 volts into the terminal interchange.
Power-On
Key: Pressing this
key turns on pc power
for the interchange.
Start
Key: This key provides a means for the oper-
ator
to start the terminal interchange
operation at the
beginning
of a work period, or after a halt.
Test
Operate Switch: Moving
this key from NORMAL
to
TEST permits transmission
of a message froma ter-
minal
set to itself. This serves
as a diagnostic procedure
to
test whether the
interchange or the
transmission line
is
at fault, in case of system
difficulties. The procedure
to
test the local interchange
is: Move the test operate
switch
to TEsT, press
the start key, and
ask an agent to
eriter
a message on the printer
keyboard. If the inter-
change
is operating
correctly, the agent’s
printer will
not
only print the information
as it is
being entered but
also
reprint it immediately
afterward, as if it were a
message
being sent
from the computer.
If there is a
duplicate
print-out of what
was entered, the inter-
change
is operating correctly.
Note that, when this
switch
is turned to TEsT, all
terminals connected to the
interchange
are prevented from
sending to or receiving
from
the data processing center.
Messages—Codes and Format
Messages
in a 9000 series system may be categorized
as input data messages, output data messages, go-
ahead messages to the interchange, go-ahead messages
to
the next interchange, and change-interchange-ad-
dress messages (from the computer).
Codes
Figure 19 shows the seven-bit
scp code for the char-
acters sent through the terminal
interchange to and
from the pushbuttons, the air information device, and
the printer keyboard. Figure 20 shows the scp code
for control signals. All characters
enter the terminal
interchange from any type of terminal as scp in serial
form. (The direct
telegraph input
and output char-
acters are discussed under “Special
Considerations for
Telegraph.”) Note that each
character is made up of
six basic data bits designated
as B, A, 8, 4, 2, 1. Addi-
tional control bits and a
check bit are added and
dropped at various
points in the system.
The character
manipulations that take place
in the terminal inter-
change are described in “Modes
and Data Flow.”
nn
6
BCD Code
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1.
Even parity within terminal interchange.
2.
Check bit dropped before
high-speed transmission
and added for low-speed
output.
3.
Shown only in Figure
6 as ticketing
buttons A,B,C, OUT.
Other action
buttons
are displayed in both
Figure 5 and Figure 6.
Note: Code for D10 is shown in Figure 20 as Type~Head Carrier Return (0001100)
Figure
19. scp Data
Code Summary for Agent’s
Set Messages
Terminal
Interchange 21
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