data
processing
center and
the peripheral
equipment
(agents’
sets,
input communication
adapters,
output
communication
adapters,
or telegraph
equipment).
Since
data
flow is similar
with all
types of
peripheral
equipment,
all types
will be called
terminals
in this
section
of the
manual. For direct
telegraph-interchange
communication,
see “Special
Considerations
for Tele-
graph”
at the
end of this section.
Each high-speed
pair
of
lines (trunk)
from the data
processing
center may
have
as many
as thirty
terminal
interchanges.
Each
terminal
interchange
may
service
up to thirty
terminals.
The
interchange
collects data
sent serially
(one bit
at
a time) from
the terminals
at low speeds
of approxi-
mately
74, 148, or 207
bits per second;
it then transmits
at
2,000 bits per
second to
the data processing
center.
IBM
1006
Terminal
Interchange
Low-
100
Telegraph
Words per
Minute--Serial
(See
Note)
|
‘
Telegraph
Speed |-
|
|
“"y
)
Equipment
Data Set
Low-
Speed
|
Data Set
Telegraph
Character
Positions--5
432
1
|
Up
to
50!
BCD
Character
Positions
--B
A8
4
2"0"
of
Cable
Era
|
The
Terminal
Interchange
(Figure
16)
is a hold-and-
On outgoing
messages
to the
terminals,
it performs
a
Agent's
Low-
;
Low-
|
;
2 ‘
:
5
5
Set
Speed
74 or 148
Bits per Second--Serial
BCD
Speed
forward
communications
information
processor.
It con-
reverse
sequence
of operations.
Figure
17
shows the
mea ie
"Nan seme
|
trols
messages
traveling
back
and
forth between
the
possible
types
of connections,
and their
speed ranges,
Set
fieie
Se
Up to
50 Feet of
Cable |
|
|
!
i
|
Figure 16. 13m
1006 Terminal
Interchange
18
to
the terminal
interchange.
No over-all predetermined
control,
timing, clocking,
or synchronization
exists be-
tween
the terminal
interchange
and the terminal.
Each
terminal
feeds immediately
into the
terminal inter-
change
and receives
immediately from it.
A typical procedure
for
handling terminal
inter-
change
transmissions
to the
data processing
center is:
The
computer
sends a go-ahead
message
(described
under
“Messages—Codes
and
Format”)
to the most
remote
terminal
interchange
on each of its
high-speed
lines.
Each most remote
interchange
transmits all mes-
sages
accumulated
since the
last transmitting
period.
At
the end of
its total transmission,
the
interchange
sends
a go-ahead
signal to the next-less-remote
inter-
change
on the line.
This process repeats
until the closest
interchange
has
completed
transmission.
This inter-
change
sends
a go-ahead signal
to the data
processing
center
which
again starts
the cycle
of scanning
with
the
most remote
interchange.
Meanwhile,
the data
processing
center
may be sending output
messages to
any
of the
terminals.
In
the terminal
interchange is a
4,000-character
storage
(with eight
bits per character
to accommodate
the
seven bits of scp
code plus an
extra control bit).
The
storage is divided
into 39 sections
for storing
data
and one section
for controls. Thus,
there are forty
100-character
sections (buffers ).
These
buffers provide
an ample assembly
area for
messages
to and from
the terminal sets.
If thirty termi-
nals
were feeding into the interchange
simultaneously,
each
would be sending, into
a (currently assigned)
buffer,
serial bits to be accumulated
up to a buffer
capacity
of 98 characters of
data for a complete mes-
sage
or for the first segment
of a long message. For
additional
segments of a
long message, the buffer
capacity is 97 data characters.
The
interchange automatically
adds two characters
to
a complete message or
the first section of a long
message.
These characters
are the terminal
address and
end-of-message.
To the follow-on
segments of a long
message,
it adds a third character—the
segment identi-
fier.
When the buffer contains
100 characters, or when
an
end-of-message is sensed
from the terminal supply-
ing
input to a buffer, the contents of the buffer are
ready
to be transmitted to the
data processing center.
Center)
Agent's
207
Bits per
Second--Serial
BCD
Set
Up to
1500
Feet
of Cable
Jp
to
Tele-
|50'of | Input
graph
Cable
|Communica-|
207 Bits
per Second--Serial
BCD
Data
Terminal
‘
nr
P| High- Bit 5 igh~
Speed
ee
Speed
Processing
Interchange
Data
Data
4 Set
High-Speed
Set
Canter
Transmission?
>
System
Equip
rt
to 1500
Feet
of
Cabl
me
Aish
Up to
1500
Feet
of
Cable
Up
to
Tele-
|50'
of |Output
i.
Cable
| Communica”
|
"207
Bits per
Second--Serial
BCD
ment
Adapter
Up
to 1500
Feet
of
Cable
Figure
17. Connections
to
the Terminal
Interchange
There
is no
permanent
assignment
of any
buffer to
any
terminal.
The buffers
are
assigned
upon demand
so
that
the interchange
can make
maximum
effective
use
of
its storage
capacity.
The
agent
is not limited
as to the
length of
message
entered
into
the terminal;
however,
each
98 (or
97) data
characters
of the
message
are transmitted
as
soon as
they
are accumulated
in their
interchange
buffer.
Out-
put
messages
from
the computer
to
the terminal
are
restricted
in length
to 100 characters,
including
termi-
nal address
and end-of-message
characters.
This
means
that,
for output
data
of more
than 100
characters,
the
program
must place
a new
terminal
address
and end-
of-message
character
in
each 100-character
segment
of
the
message,
thus
making
it appear
to
the interchange
as
a separate
message.
(The program
must
also
prefix
each
message
segment
with the
interchange
address,
but
this
character
is not
included
in the
100-character
capacity
of the message.
)
Note:
The direct
telegraph connection
is usable
only in
systems designed
to accept telegraph
code.
Because
the interchange
may be
simultaneously
servicing
all connected
terminals
and
high-speed
lines,
it
may be
operating
in
from one
to four
modes
simul-
taneously.
These
four
modes are:
receive
low-speed
(from
the
terminal),
send
high-speed
(to the
com-
puter),
receive
high-speed
(from
the computer),
and
send
low-speed
(to
the terminal).
Any
one buffer
in
the
interchange,
however,
is
operated
upon
in only
one
mode
at
any one
time.
Components
Figure
18 shows
the
general
composition
of
the
termi-
nal interchange
and
relationship
of the
components.
The
primary
components
are:
data
storage;
control
storage
for input-output
line controls,
and
other
con-
trols;
and
registers
for data
and
the
control
word.
The
arrows
represent
the
direction
or
directions
in which
Terminal
Interchange
19
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