Transmission Capability - IBM 2790 Manual

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Figure . Segmentation
Transaction Code Character. An eight-bit hexadecimal data
byte transmitted from the area station to the system con­
troller indicating which transaction key has been depressed
by the operator, and other control conditions.
Transaction Expansion. The capability of selecting one of
81 possible transactions using the normal transaction
selection switches (1-9) followed by an expansion digit
(1-9). The transaction expansion digit can be entered from
the card reader, the resident badge reader, the digital read-in
device, or the manual keyboard; however, only one device
type can be designated for each transaction selection
switch.
For the card reader, resident badge reader, and the
digital read-in device, the expansion digit is the first digit
(monitor key excluded) transmitted within the first data
entry of a transaction. For the manual keyboard, the
transaction expansion digit is also the first digit trans­
mitted; however, because the first digit transmitted from
the manual keyboard is the one that appears in the left­
most visual display position, manual keying must continue
until the transaction expansion digit has reached that
position. This can be accomplished by keying the digit
six times or by keying the digit and then using the remain­
ing five positions for data.
Area station transactions selected by transaction expan­
sion may be multiple-input data entries.
Note: Digit zero is an invalid transaction expansion
digit.
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Transaction expansion is a prerequisite for message
routing. Transaction expansion is activated when the pro­
grammer defines the transaction codes in the transaction
group (TGROUP) macro. See IBM System /360 Operating
System, Basic Telecommunications Access Method,
GC30-2004; or IBM System /360 Disk Operating System,
Basic Telecommunications Access Method, GC30-5001.
Guidance Panel A 36-position lighted display matrix
(four columns, nine rows), of which 31 positions are
available to the customer to give specific instructions to the
area station operator. The 32nd position is reserved for the
Select Transaction display. Positions 33 through 36 are
operational indicators.
Guidance Character. An eight-bit data byte transmitted
from the system controller to the area station to indicate
the operator-guidance light to be lighted, the device to be
read, and the state of the In-Process light.

Transmission Capability

The 2791 and 2793 Area Stations are connected serially by
a two-wire cable. The area stations are designed so that if
one area station is turned off or otherwise loses power,
operation of the loop is not affected. The adjacent area
station on the loop supplies power, via the loop connection,
to a portion of the inactive area station, thus maintaining
loop operation. The transmission-line rate is about 500,000
bits per second.