IBM 3741 Data Station Reference Manual page 73

Multipoint Communications
Multipoint communications allows the 3741 and other
terminal devices to communicate with a processing. unit
on a dedicated network. The 3741 on a multipoint net-
work only serves as a tributary station. The 3741 can
monitor the line at all times and respond to its own polling
and selecting sequences as appropriate. When in transmit
mode, the 3741 responds to a poll by transmitting data.
When in receive mode, the 3741 responds to selection with
a positive acknowledgement. If the 3741 is not ready to
receive, it responds with a negative acknowledgement to
selection. When the 3741 is not in communications mode,
the operator is also notified (a tone is heard) that the pro-
cessing unit has data to send and that the 3741 should be
placed in receive mode. If the 3741 is not ready to transmit
when polled, it responds with EOT. If the 3741 is ready to
transmit and is selected, it responds with RVI.
Program
Buffer
Number
Controllin g
Program Buffer 8
Program Buffer 9
Program Buffer A
First Transmitted Data Set
Second Transmitted Data Set
Third Transmitted Data Set
First Received Data Set
Second.Received Data Set
Third Received Data Set
T
- -
T
-
T
-
T
- -
T
-
8 9 A 8
9
T A transmit selected fields or records program.
R A receive data and insert constants program
-
T
T
9
A
Inquiry
This function of the Expanded Communication·s Multipoint
Data Link Control Feature allows the operator to key a
single record inquiry message, transmit the inquiry to a
remote processing unit and receive a response to the inquiry.
Both the inquiry message and the response are recorded in
a data set on disk and can be displayed by the operator.
See Inquiry Mode
(I)
and Operating Procedures for more
information.
PROGRAM TYPE IN PROGRAM BUFFER
T T R
- -
R
-
R R T T
-
T T R R R R
-
T R
-
T
-
R
-
R R
-
R R
-
T T R T
-
R T R R T
T T
- -
R
-
R R R
-
R R R R
-
T T T T T R
8 8 8 8 9 8 8 8
A 9 9
A
8 9 A 8 9 8 8 9 A AA 9 8 8 8 8 9 9 8
9 A A 9 A 9 A
A
- - Program buffer does not contain a transmit selected fields, records, or receive data and insert constants
program.
kS
Any data sets transmitted or received are not under program control.
Note: The contents of program buffers 8, 9, and A remain active after communications is complete. That is,
if communications mode is again selected, these buffers would be used in controlling the transmitting or receiving
of data. Therefore, if these program buffers are not required after their initial use for one communications pro-
cess, their contents should be deleted.
Figure 33. Expanded Communications Program Buffer Usage
Communications 67