Read and Write Operations in Transparent Mode
Transparent mode is used during reading and writing
operations of text transmitted in !!bit-patternstructure" rather than "character-pattern structure" as in normal mode.
Transparent-ReadOperation. The SF enters trans
parent mode via the control-character sequence
DLE STX. SF exits from the transparent mode of
operation by the detection of a DLE followed by any
end control character (NAK, ETX, ETB, ENQ,EOT, or ITB). A DLE followed by a non-ending control
character results in the SF remaining in transparent
mode and in the setting of sense-bit 4 (Data Check)
to one. A DLE DLE sequence causes the SF to
remain in transparent mode with the first DLE
deleted from the data sent to main storage, as is
every first DLE in transparent mode.
Transparent-Write Operation. Transparent-write
operations require two Write commands to be
executed. The first Write command is used to trans
mit the data stream and is ended normally when the
byte count equals zero. The command-chained
second Write causes the SF to leave transparent mode
when one of the following sequences is detected
during the second Write command execution--DLE
ETB, DLE ETX, or DLE ITB. The command ends
with Channel End and Device End status. If none
of these sequences occur, the byte count of the
second Write command (CCW), when decremented
to zero, causes the command to end and the SF
leaves transparent mode. Channel End and Device
End status are set.
The second Write command must be received by
the SF within three seconds of the ending of the first
Write command; otherwise a timeout occurs with
Channel End, Device End, andUnit Check status and
the Time sense bit (bit 7) set to one.
During transparent operations, the SF generates
a DLE character whenever it detects a transparent
text-bit configuration that is the same bit config
uration as a DLE character. This insertion of a
DLE prevents the receiving station from falsely
ending a block if the transparent-bit configuration is
the same as a transparent-ending sequence (e. g. ,
DLE E TX). The inserted DLE is deleted by the
receiving station prior to placing the received
message in the receiving stationI s main storage.
To permit a bona fide ending sequence to be
transmitted, the transmitting SF must know When
to inhibit the insertion of the DLE character under
the conditions just cited. This is accomplished by
the use of the two Write commands as follows.
The byte count of the first Write command is
decremented to zero'upon the transmission of the
last byte (character) of the message. The second
Write is command chained to the first Write com
mand, with the second Write command containing the
ending sequence. Thus the SF recognizes the ending
of the first Write command as the initiation of the
ending sequence provided by the second Write.Under this second Write command, the SF does not
generate a DLE upon detection of a main-storage
provided ending sequence. See Figure 15.PROGRAMMING NOTES: For both read and write operations, a
DLE ITB sequence causes theSF to exit from transparent mode,
yet continue in text mode
TheSF sends the block-check-character accumulation after
ETB, ETX, or ITB.
The DLESYN sequence is used in transparent mode in the same
manner that theSYN is used in nontransparent mode. The
DLESYN sequence is not recommended for use as time-fill.
In transparent operations, no VRC checking follows the initial
DLESTX se quence except on control characters.
The DLE ITB sequence is followed by the beeSYN SYN (double SYN generated by the equipment) sequence. If the data follow
ing is to be in transparent mode, the DLESTX sequence must
follow theSYN characters. In this case, the DLE and STX characters are included in the bcc accumulation.
Search
This command is used when the synchronous-equipped2703 is operating as a master station. The Search
command may be issued only after aPoll command.
Searchccw DE, f I, f 2, f 3 I DE I Data Address I D 78 31 Count
32 78 4748
Since the SF will normally be in character phase
when the Search command is issued, data will be
immediately transferred to main storage, starting
with the last index character 9 sent from main
storage under the precedingPoll command). The
last index character is followed by the data being
received from the communications line.I 63
All data received before going into text mode
(entry into text mode via recognition of the STX orSOH --including the first STX or SOH) is sent to main
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Transparent mode is used during reading and writing
operations of text transmitted in !!bit-pattern
Transparent-Read
parent mode via the control-character sequence
DLE STX. SF exits from the transparent mode of
operation by the detection of a DLE followed by any
end control character (NAK, ETX, ETB, ENQ,
character results in the SF remaining in transparent
mode and in the setting of sense-bit 4 (Data Check)
to one. A DLE DLE sequence causes the SF to
remain in transparent mode with the first DLE
deleted from the data sent to main storage, as is
every first DLE in transparent mode.
Transparent-Write Operation. Transparent-write
operations require two Write commands to be
executed. The first Write command is used to trans
mit the data stream and is ended normally when the
byte count equals zero. The command-chained
second Write causes the SF to leave transparent mode
when one of the following sequences is detected
during the second Write command execution--DLE
ETB, DLE ETX, or DLE ITB. The command ends
with Channel End and Device End status. If none
of these sequences occur, the byte count of the
second Write command (CCW), when decremented
to zero, causes the command to end and the SF
leaves transparent mode. Channel End and Device
End status are set.
The second Write command must be received by
the SF within three seconds of the ending of the first
Write command; otherwise a timeout occurs with
Channel End, Device End, and
the Time sense bit (bit 7) set to one.
During transparent operations, the SF generates
a DLE character whenever it detects a transparent
text-bit configuration that is the same bit config
uration as a DLE character. This insertion of a
DLE prevents the receiving station from falsely
ending a block if the transparent-bit configuration is
the same as a transparent-ending sequence (e. g. ,
DLE E TX). The inserted DLE is deleted by the
receiving station prior to placing the received
message in the receiving station
To permit a bona fide ending sequence to be
transmitted, the transmitting SF must know When
to inhibit the insertion of the DLE character under
the conditions just cited. This is accomplished by
the use of the two Write commands as follows.
The byte count of the first Write command is
decremented to zero'upon the transmission of the
last byte (character) of the message. The second
Write is command chained to the first Write com
mand, with the second Write command containing the
ending sequence. Thus the SF recognizes the ending
of the first Write command as the initiation of the
ending sequence provided by the second Write.
generate a DLE upon detection of a main-storage
provided ending sequence. See Figure 15.
DLE ITB sequence causes the
yet continue in text mode
The
ETB, ETX, or ITB.
The DLE
manner that the
DLE
In transparent operations, no VRC checking follows the initial
DLE
The DLE ITB sequence is followed by the bee
ing is to be in transparent mode, the DLE
follow the
Search
This command is used when the synchronous-equipped
command may be issued only after a
Search
32 78 4748
Since the SF will normally be in character phase
when the Search command is issued, data will be
immediately transferred to main storage, starting
with the last index character 9 sent from main
storage under the preceding
last index character is followed by the data being
received from the communications line.
All data received before going into text mode
(entry into text mode via recognition of the STX or
59