Table of Contents
Advertisement
Multiplexer
© CD
NON-
SWITCHED
LINE
Terminal
A
D
D
S
R
E
s
5
I
1
P
A
C
E
@
G)
L
L
®
R
R
Text
C
Text
®C
©
i
1
0
0
or
or
Figure 34. Station Control, i\lultiplexer Addressing (with Checking Special Feature)
of the status of the m aster terminal.
A subordinate
terminal without status does not receive the message.
Addressing l\lode Sequence. Turning power on in the
terminal places the terminal in text non-selected·
mode and only the receipt of a
©
can change this
mode. A
<0
places the terminal in control receive
mode (Figures 33 and 34) in which the terminal can
recognize a
@, @,
or any alphabetic address char-
acter. Because the address is being received, the
next character received is the
®
which indicates
that the terminal is being addressed, not polled, a:t1d
places the terminal in control address mode.
In
con-
trol address mode, the terminal can recognize a
©,
@'
terminal address, group address, or an all call
address. When a terminal address is received, the
following events occur.
The terminal address is rccognized and places the
terminal in control address selected mode. Only the
terminal that is wired for the received address char-
acter changes mode; unselected terminals remain in
control address mode until rpcciving a
©
or
@.
Next in the addressing sequence is the space char-
acter, which places the terminal in transmit status
answerback mode.
In
this mode, the status of the
terminal is checked and a
®
or
®
sent to the mul-
tiplexer. The
@
indicates to the multiplexer that
the terminal does not have status and therefore the
computer message should not be sent. An alarm bell
rings to indicate that the terminal was addressed. A
®
sent from terminal to multiplexer indicates that
the terminal has
s~tus
and the' message can be sent.
The
®
places the terminal iIi control selected mode
awaiting the first character of the message (which
shou~d be a
@ ).
If the multiplexer sends a
©.
the terminal enters control rwceive mode. The
@
places the selected terminal in receive text mode and
the non-selected terminals in text non-selected mode.
If the selected terminal loses status during the mes-
sage, the selected terminal is also placed in text non-
selected mode. A
©
follows the multiplexer mes-
sage, indicating to the terminal that the message is
completed and placing the terminal in control receive
mode.
If a group or all call address is received, the fol-
lowing sequence 'of events occurs.
Events up to control address mode are the same
as for a terminal address. In control address mode.
however, the group or all call address is recognized
by more than one terminal. Only the master termi-
nal can transmit an answerback; all other, terminals
(subordinate) are prevented from answering. The
master performs exactly as when an individual ter-
minal address is received but the subordinates per-
form differently. If the subordinate has status, it goes
to control address selected subordinate mode; if the
terminal does not have status, it remains in control
address mode and is inactive until a
©
or
@
is
received placing the subordinate in text non-selected
mode or control receive mode. respectively.
Polling Mode Sequence: As in addressing, the termi-
nal is placed in text non-selected mode when power
is turn~d on. Receipt of the
©
in the polling se-
quence (Figures 35 and 36) places the terminal in
contTol receive mode. As in addressing, a
© '
@ ,
®,
or addreSSing character can be received
in control receive mode.
Because this is a polling
operation. the character received is an address
character which places the terminal in intermediate
polling mode. In this mode, the bid circuit is
checked to see if the bid key had been pressed.
When
th~
space is received, if the bid key had been
pressed the terminal goes to transmit text mode
and a@ is sent to the multiplexer; the operator
then transmits the message. If the bid key was not
pressed, the terminal enters transmit poll
29
Advertisement
Table of Contents
