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carrier tra\·el. Round off the result to the next
higher. whole number.
Carrier Return:
N = T
+
1. 5
Tab:
N=T·1.G
Index:
N = 1
. The keyboard speed varies according to the operator
tor's typing ability, with the maximum speed not to
exceed 1-1.8 cps (characters per second). See
.
"Terminal Transmission and Control Speed" below.
Data-Handlin~
Capability
To compute the data-handling capability
\)f
the 27·to
terminal, the
follo~\"ing
basie timings
~ust
be con-
sidered. They represent terminal timings only and
do not include timings for operations in the computer
and the transmission control unit.
Terminal Transmission and Control Speed
The speed of the 2740 terminal is 133.2 to 135.6 bits
per second. Each character consists of a start bit
six data bits, a check bit, and a stop bit. Because'
each character contains nine bits, the character
time is 66.
-l
to 67. 6 milliseconds per character, the
bit time is 7.37-7.51 ms, and the speed of the termi-
nal is 14.8 to 15.1 characters per second. IBM usu-
ally states the most conservative speed in this range,
namely 14.8 characters per second; the character
time as 67.5 milliseconds per character; the bit rate
(nine bits per character) as 133.2 bits per second;
the bit time as 7.51 ms.
Addressing Time
The time required to address a terminal (2185 ms)
is calculated as follows:
(6 x 67.5)
+
1780
=
2185 ms
(6 x 67.5) :; 6 character times
(© , ® ,
address,
space, response, and
@ ).
1780
=
Delay before transmission of response, in-
cludes data set turn-around time and time
required for the typewriter motor to reach
full speed.
It
does not include any delays
at the multiplexer, such as between re-
sponse and
@ .
Polling Time (Negative
Answ~rback)
T~e
time required for a polling operation witn a neg-
atIve answerback (600 rns) is calculated as ,:follows:
20
(4 x 67.5) +' 330*
=
600 ms
.
'.
•
(4
x
67.5) = 4 character times
(© ,
ad-
dress, sJl8:ce, and
®
response).
3:JO* .. Delay before transmission of re-
sponse.
Polling Time (Positive Answerback)
The time requi red for a polling operation with posi-
tive answerback
(fiOO
ms) is calculated as follows:
(4 x
67.3)
.+
:~:W*
=
600
ms
(..t
x
li7.
:» -
4
character times
(@'
addr<!ss.
space, and
@
response).
Checking Time (Reeei\'e Terminal, Positive Answer-
back)
The time required for checking at the receiving
terminal with a positive answerback
(;):~:~
rns) is
calculated as follows:
(3
x 67.
5) +
a~w*
;=
533 ms
(3 x
67. ;)
=:
3 character times
(®
,LR
C,
and
(X)
response).
330*
:0:
Delay before sending response.
Checking Time (Receive Terminal, Negative Answer-
back)
The time for checking at the receiving terminal with
a negative answerback is calculated as follows:
(3
x
67.5)
+
135
+
330*
+
(N
x
67.5) = 668
-!-
(N
x
67.5) ms
(3
x
67.5)
=
3 character times
(®,
LRC,
and N response).
135
;=
Time required for the terminal to
print the negative indication.
330*
=
Delay before transmitting response.
(N
x
67.
5)
=
Time required for the type-
writer to perform the CR/LF
function.
N
=
The number of inches the carrier must
return
if
the @signal was initiated by
pressing the return key (auto EOB).
Any fraction of an inch is considered a
whole inch.
Checking Time (Transmit Terminal, Positive Answer-
back)
The time required at the transmitting terminal awai t-
ing a positive answerback from the receiving termi-
nal (203 ms) is calculat.ed as follows:
(3
x
67. 5)
=
203 nis
*This. figure may vary depending upon the type of data
set used and how it is connected .
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