Summary Of Sequences And Responses; 2845 Display Control Sequences And Responses; Start Of Text (Stx); End Of Text (Etx) - IBM 2265 Manual

Table 6 lists the 12 (or 15) possible line addresses.
Note that only the byte formats listed in the table should
be used to select display lines.
PROGRAMMING NOTE: All messages sent under
th~s
command
must contain the line address immediately following the STX
character. Since the line address character is not displayed, any
other character sent in its place will be lost. Therefore, unlike
other commands, this command cannot be converted to the Write
Addressed DS command without sending a complete Write Ad-
dressed DS command addressing sequence.
SUMMARY OF SEQUENCES AND RESPONSES
The sequences and responses that occur between the I/O
channel and the 2845 Display Control are composed of
seven of the eight USASCII communication control char-
acters. These characters, used singly or in sequences,
facilitate or are directly responsible for the following:
1. Perform line control functions.
2. Maintain operational continuity.
3. Provide the I/O channel with the current status of the
operation of a specific device.
4. Signal the detection of an error or unusual condition to
Hie I/O channel or the 2845 Display Control.
5. Provide the I/O channel with specific information re-
garding an error or unusual condition.
The significance of a given sequence or response may
differ depending on the operation and receiver; i.e., a
specific response received at the 2845 may be interpreted
differently than the same response directed to the I/O
channel. Thus, the sequences and responses are described
for both their significance to the I/O channel and
t~
the
2845 Display Control.
Table 6. Display Line Addresses
2845 Display Control Sequences and Responses
Ail line control characters recognized during execution of
a Read command issued to the I/O channel are transferred
to main storage. The following communication control
characters sent by the 2845 are recognized by the 2701
during execution of an I/O channel Read command:
Start of Text (STX)
The STX communication control character is the first
character of a message sent by the 2845 in response to the
Read Addressed Full DS Buffer and all poll commands.
The STX character initiates, but is not included in, the
LRC accumulation in both the 2845 and the 2701. The
character following the STX is always the address of the
device.
End of Text (ETX)
The ETX communication control character signifies that
the last text character of the message has been transmitted
and indicates the following character is the LRC character.
ETX initiates line turnaround at the 2701 after receipt of
the LRC character. The ETX character is included in the
LRC accumulation. Upon receipt of ETX and the LRC
character, the 2701 performs an LRC accumulation check.
At the conclusion of the LRC check, Channel End and
Device End are set in the 2701 status byte, and the status
byte is transferred to the I/O channel. If an LRC or VRC
error is detected in the transmission, Unit Check is also set
in the status byte, and Data Check is set in the sense byte.
Cancel (CAN)
The CAN communication control character signifies that
the transmitted text may contain characters with 2845-
USASCII-8 Data Byte Format Hexadecimal Representation Selected Display Line
Bits
8 7 6 5 4 3 2
1
0 1 0 1 0 0 0 0
50 1
-
-
0 1 0 1 0 0 0 1
51 2
0 1 0 1 0 0 1 0
52 3
0
1 0
1 0 0 1 1
53 4
0 1 0 1 0 1 0 0
54
5
0 1 0 1 0 1 0 1
55 6
0
1 0 1 0 1 1 0
56 7
0
1 0 1 0 1 1 1
57 8
0 1 0 1 1 0 0 0
58 9
0 1 0 1 1 0 0 1
59
10
0 1 0
1 1 0 1 0
5A 11
0 1 0 1 1 0 1 1
5B 12
-
0 1 0 1 1 1 0 0
5C 13
0 1 0 1 1 1 0 1
50 14
0 1 0 1 1 1 1 0
5E 15
42