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:
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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.

The following introduction to start/stop (asynchro­
nous) type operations uses as examples IBM type terminals, such as the 1030, 1050, 1060, and 2740. The transmission of data by means of start/stop
type communications involves, for example, the
coding of each character with a start bit and a stop
bit, in addition to the data bits and possibly a check
bit for odd parity such as shown in Figure 5. Thus,
the transmission of characters can occur at an
irregular rate, since each character contains its own
sync information (character timing). This is parti­
cularly useful for transmission from unbuffered
units such as keyboards and devices requiring the
manual insertion of input documents (badge readers,
card readers, etc.). Start/ stop communications require the use of a
unique set of line-control characters to provide for
communications-line discipline (polling and addres­
sing) and identification of the various portions of the
message (station identification, text blocks, etc.).
All messages are transmitted during text mode,
after certain control operations are first performed
in control mode. All characters transmitted during
text mode are either printable data characters or
functional characters (not printable). The functional
characters consist of such codes as CR/LF, delete,
and idle. Codes transmitted during control mode provide
terminal control, station identification, and component
selection for the remote terminal. For example, the 1050 uses a line-control signal, © --EOT, and
an alphabetic station-identification character and a
numeric component-select code (together with the
appropriate response) to maintain communications­
line discipline. These polling and addressing pro­
cedures allow the 2703 to control the communications
line at all times. Messages transmitted from the 2703 are preceded by an address. Remote stations
have the opportunity to transmit only when polled
from the 2703. *8 Indicates no 8-bit
Figure 5. Bit Configuration of a "G" Character
(Serialized) START/STOP COMMUNICATIONS CAPABILITIES LINE CONTROL The following are transmitted during control mode: • Control signals--EOT, EOA, EOB, Yes, No, SOA, and Inquiry. • Polling characters--These consist of an alpha­
betic station -identification character, A - Z ,
followed by a numeric component-select
character (used by the 1050), 5, 6, 7, or o.
The polled terminal is requested to transmit,
if the polled component is ready. • Addressing characters--These also consist of
an alphabetic station-identification character, A-Z, followed by a numeric component-select
character (used by the 1050), 1,2,3,4, or9.
The addressed terminal is requested to receive,
if the addressed component is ready.
The line-control signals--EOT, EOA, EOB, Yes,
No, SOA, and Inquiry--are represented in a short­
hand form--© ' CD , @ , (i) , ® , ® ' and @ , respectively (Figure 6). form is used in
programming as well as in communications and line­
control discussions. Also, the terms "response" and "answer" are used in the following restricted manner:
1. Answcr--The negative or positive reply, or no
rep.1y at all, to an LRC compare.
2. Response--The negative or positive reply, or
no reply at all, to a component-select charac­
ter (addressing or polling).
Description Symbol Processor Bi t Processor Configuration Character End of Transaction (EaT)
© C-8-4-2-1 r(TapeMark) End of Address (EOA) @ 8-2-1
# (Pound Sign)
End of Block (EOB) ® C-A-8-4-2 't (Record IV Jrk) Positive Response (YES) G) B-A-8-2-1 (Period) Negative ResponsE' (NO) @ B -(Hyphen)
Address Select (SOA) CD C-A-8-2-1 , (Comma) Positive Response (Inquiry) 0 8-2-1 it (Pound Sign)
Figure 6. Line-Control Characters
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