Eob (End-Of-Block) Key (Checking Special Feature); Automatic Eob (Prerequisite, Checking Feature) - IBM 2740-1 System Reference Manual

The Dial-Connect light on indicates that the
terminal originating the dial connection is connected
to a remote terminal and is in standby status (com­
municate mode). The Dial-Connect light at the
remote terminal also turns on when the connection
is established and turns off when the terminal shifts
to transmit or receive status.
terminal goes into the transm it or receive status,
this light turns off and the Transmit or Receive
light turns on.

EOB (End-of-Block) Key (Checking Special Feature)

This key is used to signal the end of a unit-block
of text. Pressing this key (Figure 4) initiates a
signal that causes the block of text just transmitted
to be checked at the receiving terminal.
does not provide an indication of accuracy as a
typist, since typed copy can be checked, but it does
ensure that all characters that were typed on your
keyboard have reached the receiving terminal cor­
rectly.
Immediately following the operation of the EOB
key, the R estart light turns on and the status lights
change from transmit to receive momentarily, and
then back to transmit, indicating that checking has
been completed. If an erro r occurred, the R estart
light remains on and the keyboard locks.
the R estart key turns the light off, unlocks the key­
board, and allows you to retransm it the message (if
necessary), or to continue message transmission.
Pressing the EOT key also turns the light off, causes
a (c) to be transmitted, and places the terminal in
control receive mode. If the message was received
correctly, the R estart light turns off automatically.

Automatic EOB (Prerequisite, Checking Feature)

Included with this feature is a three-position switch
Auto Ck (auto check) located on the left side of the
2740 cabinet (Figure 1).
of the switch are: Term (terminal), Mplx (multi­
plexer), and Off. Set the switch to Term when
transmitting to another terminal and to Mplx when
transmitting to a multiplexer.
to Term or Mplx, each operation of the Return key
causes the ca rrie r to return and the EOB/LRC se­
quence to be transmitted automatically, thereby
causing the line of characters just transmitted to
be checked at the receiving terminal.
shifts momentarily from transmit to receive status
(Transmit light turns off, Receive and R estart lights
turn on). If the receiving terminal responds with a
positive answer, your terminal shifts back to trans­
mit status (Transmit light turns on, Receive and Re­
start lights turn off, and keyboard unlocks) and you
can continue with message transmission.
When the originating
This check
Pressing
The three positions
With the switch set
Your terminal
If the message is received incorrectly, the r e ­
ceiving terminal prints a hyphen (below the message
block just completed) and a negative response is sent
back to your terminal. This negative response
causes a hyphen to print (below the message block
just completed) at your terminal.
sponse also locks your keyboard, turns the Transmit
light on, sounds the audible alarm, and causes the
R estart light to remain on.
retransmitted by pressing the R estart key. Opera­
ting this key turns the Restart light off, causes a
CR/LF (carrier return and line feed) to occur at
your terminal, and another CR/LF to occur at the
receiving terminal if the switch is s e t to the Term
position. If the switch is set to the Mplx position,
the CR/LF code is not transmitted to the receiving
terminal. The CR/LF operation positions the
carrier on a new line (below the hyphen). The mes­
sage can now be retransmitted.
When the switch is set to Off, the EOB key must
be manually operated to initiate a record check (see
Automatic EOB under Special Features, Model 1).
Figure 4. IBM 2740 Model 1 Transmission Controls (Left Side of
Keyboard)
Transmission Controls and Indicators, Model 1
The negative r e ­
The message can be
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