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Special Characters - IBM 2702 Information Manual

Transmission controls
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Mark
b!.fBi -
Space. _ _ _ _ _ _ _ Start
B
A
I-~,I
'
8 : 4 I 2
LI.J
C :Stop )
Example character
B---2-C
Start Bit always space level
Stop Bit always mark level
I ,
) : L
Figure 2-20. IBM Terminal Control Type I Transmission Code
bit) in the shift-bit position signals a lower-case
character, while a 1 (bit) signals an upper-case
character.
During a write operation, the terminal control
monitors this bit position in data received from the
I/o
interface. When the terminal control detects a
change in case in the data characters, it inserts an
upshift or a downshift character into the transmitted
data stream.
During a read operation, the terminal control
monitors the received characters for the upshift
or downshift character, deletes the upshift or down-
shift character from the data stream, and inserts
a 0 or 1 in the I/O interface byte position
O.
VRC (Vertical Redundancy Check)
The IBM Terminal Control Type I checks each
received and transmitted character for odd vertical
parity. VR C errors cause Data Check to be set in
the sense byte, but do not cause termination of the
command currently being executed.
LR C (Longitudinal Redundancy Check)
The IBM Terminal Control Type I has the ability to
do longitudinal redundancy checking. This checking
is done by accumulating a binary count for each data-
character bit position. Each bit-position count is
accumulated separately without carries into other
pOSitions. The sending station's accumulated LRC
total is sent as the last character of the data block.
The LR C character from the sending station should
match the LRC accumulation at the receiving station
if no bits were lost in transmission.
I
p
I
0
1
2
3
4
5
6
:Shift
B
A
8
4
2
1
I
I
Shift bit 0 (lower case) or 1 (upper case)
inserted on receive operations or deleted on
transmit operations. Insertion/deletion is
performed by equipment.
7
I/O
Interface Date Byte.
Transmission Code.
C
Figure 2-21. IBM Terminal Control Type I Transmission to Interface
Conversion
2-40
Not all terminals can do an LR C check. Special
characters signal when to start an LRC accumulation
and when the LR C accumulation should equal zero.
Special Characters
Figure 2-22 presents the code configurations for
special characters.
Transmit
Line-control characters recognized by the IBM Ter-
minal Control Type I during transmit operations
follow.
@--End of Block (EOB). Indicates the end of a
block of text. The LRC character, developed by
the adapter (in concert with the terminal), is trans-
mitted immediately after the
®.
After the adapter
transmits the LR C character, Channel End and
Device End status is set, provided no error condi-
tions have been detected.
(If
the two LRCs differ,
the Data Check sense bit is also set.)
©--End of Transmission (EOT). Indicates the end
of transmission. This control character places the
line control (the terminal control for the particular
line in question) in control mode. While the line
contrQl is in control mode, the character case
(upper or lower) is effectively lower-case or down-
shift mode. The
©
does not end a write-type com-
mand. The © resets the LR C counters at both the
transmitting and receiving locations.
Interface Code
Transmission Code
Special Character
Pos 0-7
BCD
®
00111101
-A842-C
©
XOOll1ll
--8421C
@
X0010ll0
--8-21-
~
Xl110110
BA8-21-
@
Xl000000
B------
Upshift
--842--
Downshift
BA842--
Delete
Xll1llll
BA8421C
Idle
Xl0llll0
B-8421-
Figure 2-22. Special-Character Configuration

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