Read and Write Operations in Transparent Mode
Transparent mode is used during reading and writing
operations of text transmitted in !!bit-pattern structure" rather than "character-pattern structure" as in normal mode.
Transparent-Read Operation. 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, and Unit 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 station I 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 the SF to exit from transparent mode,
yet continue in text mode
The SF sends the block-check-character accumulation after
ETB, ETX, or ITB.
The DLE SYN sequence is used in transparent mode in the same
manner that the SYN is used in nontransparent mode. The
DLE SYN sequence is not recommended for use as time-fill.
In transparent operations, no VRC checking follows the initial
DLE STX se quence except on control characters.
The DLE ITB sequence is followed by the bee SYN SYN (double SYN generated by the equipment) sequence. If the data follow­
ing is to be in transparent mode, the DLE STX sequence must
follow the SYN characters. In this case, the DLE and STX characters are included in the bcc accumulation.
Search
This command is used when the synchronous-equipped 2703 is operating as a master station. The Search
command may be issued only after a Poll command.
Search ccw 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 preceding Poll 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 or SOH --including the first STX or SOH) is sent to main
59
Transparent Operation - 2703 Main Storage Transmitting
Transmitting Station
(Moin Storage Contents)
Moin Storage
Receiving Command fl,f2,h WR n,40,99 WR n + 1 00, 00, 1
byte location Location n J n+ n+ n+ 'f 99, 100, 101 Q Q Q Q Q Q Q Q \\ Q Q Q Q Q Q OLE Q (2 Q Q Q Q \\ Q Q Q Q Q Q OLEETX Transmitted Via
1st Write Command SF enters transparent
mode
[ 100 bytes (Characters)]
byte
count = 0 2nd Write
Command
(Contains
End
Sequence)
byte count = 0 (When detected,
Character Stream thru transmitting SF and over communication facility SF leaves Transparent mode.)
OLESTX Q Q Q Q Q Q Q Q \\ Q Q Q Q Q Q OLEOLE Q Q Q Q Q Q Q \\ Q 6 Q Q Q Q Q OLEETX L Leading character by
across line transmitting
Receiving Station
(Main Storage Con.cnts) (thru receiving station SF and into main storage) SF prior to
transmission Location XI OLESTX Q Q Q Q Q Q Q Q \\ Q Q Q Q Q Q LReCeiVing
,Byte t.ecation x + 100/ tOLE Q Q Q Q Q Q Q \\ Q Q Q Q Q Q Q ETX SF enters
transparent
mode
1 st OLE deleted by
receiving SF prior to storing deleted at SF Q Any transparent bit configuration
Figure 15. Transparent Operation
storage. Before going into text mode, the one­
second timeout is utilized and the timeout condition
is reset every time a new End character, STX or SOH, is detected. If the one-second-timeout condi­
tion is recognized before entry into text mode, the
Search command ends with Channel End, Device
End, and Unit Check status (CSW bits 36, 37, and 38)
and the Timeout bit (sense-bit 7) set to one. While
in text mode, no data is sent to main storage and
the SF monitors all data and responses. The GO Search command ends with Channel End, Devicc
End, and Unit Exception status (CSW bits 36, 37,
and 39) upon recognition of an EOT character, or
with Channel End, Device End, and Unit Check
status (CSW bits 36, 37, and 38) and the Timeout
sense bit (bit 7) set to one if the three-second
timeout occurs after entering text mode.
If the first non-SYN character received as a
response to a Poll command was a master-station
address, the Search command chained to the Poll
Previous Page Next Page