Autocall Feature
The Autocall (automatic calling) special feature pro­
vides the 2703 with automatic dial-up capability
under the programmer I s control. Each Autocall fea­
ture services up to eight dial connection lines, one
at a time, on a time-shared basis. A maximum of. two Autocall features is permitted with anyone 2703. When either of the Autocall features is used with
a Synchronous Line Set, the Autocall feature can
accommodate two such line sets (eight BSC lines).
However, any such Synchronous Line Sets that share
an Autocall feature must adhere to the following:
1. Both Synchronous Line Sets must be on the
same Synchronous Line Base;
2. Both must have consecutive addresses;
3. The first Synchronous Line Set of the two must have its initial address assigned to an address
boundary that is a multiple of eight.
The programmer initiates the automatic-calling
function whe:l 11e issueq a Dial command to an
appropriate 2703 line address. On acceptance of
the Dial command, the bytes (dial digits) are received
from the multiplexe r channel in the same manner as
any other bytes of output data, and are transferred to
common-carrier dial equipment. The dial digits
transferred from the multiplexer channel to the 2703 have the following hexadecimal code represen­
tation:
Dial Digit Hexadecimal Code
1 01 2 02 3 03 4 04 5 05 6 06 7 07 8 08 9 09 0 00 NOTE: The 2703 Autocall feature does not check to see that the ch;lr;lcters tr;lnsmitted under a Dial command are valid dial
digits.
The dial digits (bytes) continue to be transferred to
the dial equipment until the channel signals stop in
response to a dial-digit request from the 2703. This
terminates the automatic-calling function and frees
the Autocall feature to initiate calling on another line.
Command chaining to a Read or Write can be
utilized, depending on the terminal type and line­
control uses. At completion of the transmission,
the call to the remote device is terminated when a
Disable command is issued.
Before issuing a Dial command to a dial-access
line, a Disable command should be issued to the
communications line to prevent the automatic­
answering function from being initiated by a terminal.
If automatic answering on the line is desired after
completion of the transmission initiated by the
automatic-calling operation, an Enable command
must be issued after the call is terminated.
The time required to establish a connection is
determined by common-carrier equipment and mav
vary significantly. For example, for a 10-digit
number--i. e., area code (3 digits), office code
(3 digit::;), and line number (4 digits) --rotary (dial
pulse) may require as much as 30 seconds, while pUdhbutton (tone) dialing eqUipment may require only 10 seconds.
Automatic Answering
Automatic answering of incoming calls is standard
on any 2703 provided with a Data Line Set or Synch­
ronous Line Set and the appropriate common-carrier
data set. This feature permits programmed control
over the automatic-answering capability of the 2703. To permit automatic answering of calls, an Enable
command must be issued to the appropriate line
address. A Disable must be issued to inhibit auto­
matic answering on any line tL ..... t has been issued an
Enable.
Command chaining can be utilized when a call is
answered. The command chained to may be either
a Read or a Write, depending on the terminal type
and line control used (to accept data or to poll the
calling terminal). To terminate the call when trans­
mission is completed, a Disable command is issued.
To allow further calls to be answered from this line
automatically, the Enable command must be reissued. NOTE: The Autocall feature is not needed or used for the
automatic answering of calls on a switched network.
Two-Processor Switch (TPS) Feature
This special feature allows the 2703 to be attached
to the multiplexer channels of two IBM System/360
processors. However, operations can occur with
only one processor at a time. The Two-Procesfor
Switch (TPS) may be used in one of three states:
neutral, channel "one" attached, channel "two" attached. When in the neutral state, the 2703 monitors both channel interfaces. The TPS is
available to the first channel that selects it. When
a valid 2703 address is decoded, the entire 2703 attaches to the channel that made the selection. Any
signals coming from the unattached channel are by­
passed by the 2703 TPS. The address group(s) valid
21

for attachment to channel "one" may be different
from the address group(s) valid for attachment to
channel "two. " Only the attached channel can cause the TPS to
automatically return to the neutral state. \Vhen the
switch to the neutral state occurs, the entire 2703 is
involved (all lines). This return to neutral may be
accomplished by one of two automatic methods:
1. If a system reset is signaled by the attached
channel, the TPS unconditionally returns to the
neutr al state.
2. If a Release command is issued by the attached
channel to any of the valid 2703 addresses for
that channel and the command is honored, the TPS returns to the neutral state. To honor the
Release command, the 2703 must be "command­ free" (no line executing a command). If it is not
command-free, it will respond to initial selec­
tion by setting Channel End, Device End, and Unit Exception and will not go to the neutral
state (see Note 2).
Two manual methods whereby the operator may
switch to the neutral state through manual interven­
tion are:
22
1. A power-on reset, initiated by pressing the
Power-On pushbutton, causes the TPS to uncon­
ditionally return to the neutral state.
2. If the Meter switch on the operator's panel is
switched to the OFF position, the TPS causes
the 2703 to go off-line only when the attached CPU is in a halt or wait state and the 2703 is
command free. After going off-line, the TPS re­
turns to the neutral state. If the TPS is in a neu­
tral state, the 2703 will become unavailable when
both CPU-l and CPU-2 come to a wait state and
the meter switch is in the OFF position. While
the Meter switch is in the OFF position, the TPS cannot be set to an attached state with either
channel. When the Meter switch is ON. the 2703 will go on-line when both CPU-l and CPU-2 are
in a halt or wait state,
The TPS feature is activated by two manually
operated partition switches on the operator's panel (CPU-lON/OFF and CPU-2 ON/OFF). These
switches permit the operator to initiate a partition
(cutoff) of either processor. These switches can
be operated for partitioning at any time, but are
effective only when:
1. The 2703 is in neutral state,
2. The CPU reaches a halt or wait state, with the
partition switch for the CPU to be partitioned (CPU-lor CPU-2) set to OFF. NOTES: 1. If both CPU-l and CPU-2 are partitioned, the 2703 is
effectively off-line relative to system availability.
2. The 2703 requires a variable length of time from the
sending of the ending status condition to the channel, until
detection of the command free state is accomplished. The
maximum time period required for detection of the command
free state is influenced by the type of Start/ Stop base installed
in the 2703, as follows:
Start/ Stop Base Type 1--11 ms. max.
Start/ Stop Base Type II--4 ms. max.
If the Release command is presented to the 2703 too soon
following the execution of the last command, the Release
command will not be honored, since the 2703 will appear to
the program as not being command free. In addition,
Release should be issued under a unique Start I/O instruction
with no command chaining.