Transmit-Transparent Mode (P); Receive Mode (R) - IBM 3742 Reference Manual

Transmit-Transparent Mode (P)
The transmit-transparent mode is used to transmit over the
communications lines all 256 EBCOIC bit combinations as
data. After loading the disks, an operator can place the
3741 in a transmit-transparent mode by pressing FUNCT
SEL upper, COMM, and P. A P will then be displayed on
the status line of the CRT display to indicate the transmit-
transparent mode.
This mode of operation is identical to the transmit mode
with the exc.eption that data is transmitted in transparent
mode. PI indicates an incompleted transparent trans-
mission; PT indicates a completed transparent transmission.
Receive Mode (R)
The receive mode is used to receive data from a remote
location and store that data on one disk or two disks (if
the second disk feature is installed). After loading the
disks, an operator can place the 3741 in receive mode by
pressing FUNCT SEL upper, COMM, and R. An R will
then be displayed on the status line of the CRT display to
indicate the receive mode.
The 3741 can ttJen be connected to the telephone line
through a modem and subsequently receive data from the
remote location and store it on the disk(s).
Oata records received with an STX are received in the non-
transparent mode; records received with a OLE STX are
received in the transparent mode.
BOE EOD
The labels for the data set to be received must be valid
HOR1 (or bypassed) labels and must not be deleted. The
BSCA feature will modify the following fi.elds of the label:
Record Length: The record length is determined from the
length of the first record received in the data set if the disk
was positioned on the data set label when the operator
selected communications mode. If the disk was positioned
on a record within the data set, the record length is deter-
mined by the record length specified in the corresponding
label.
Beginning of Extent: The beginning of extent (BOE) is
not changed on the label of the first data set received and
is made equal to the end of data (EOO) of the previous
data set for all succeeding data sets received. (See Figure
29 for summary of extents generated during receive mode
operation. )
End of Extent: The end of extent (EOE) address is made
equal to the record address of the last recorded record.
End of Data: The end of data (EOO) is made equal to the
end of extent plus 1, except when a null data set is
received. In this case, the end of data and end of extent
are made equal to the beginning of extent address.
Multivolume Indicator: The multivolume indicator of the
first disk is changed to a C (continued data set) when the
overflow of the first disk is written on the second disk. The
multivolume indicator of the second disk is changed to an
L to indicate the last disk of a continued data set. All
other label information is left unchanged.
EOE
First received data set on BOE of the label BOE
+
number of
EOO - 1 (if null data
first disk records received
set, EOO)
Succeeding data sets on Previous EOO BOE
+
number of
EOO - 1 (if null data
first or second disk records received
set, EOO)
First data set following Previous EOE
+
1 BOE
+
number of
EOO - 1 (if null data
a transmitted data set
records received set, ECJO)
on first or second disk
First received data set 01001 BOE
+
number of
EOO - 1 (if null data
I
on second disk
records r·eceived set, EOO)
Figure 29. 3741 Model 2 Generated Extents while in Receive Mode
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