IBM System/34 Maintenance Manual page 452

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'--..-/
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30-660 EIA/CCITT Modem Control Lines
The modem control lines for the EIA/ CCITT interface
are active during the up level. These lines and their
associated pin numbers are shown in Figure 30-26. The
following paragraphs describe eight of these lines.
The ' RTS' (request to send) line controls the transmit
and receive functions of the modem. When this line is
active, the modem is in transmit mode; when this line is
not active, the modem is in receive mode. On a 2-wire
nonswitched line, 'RTS' is switched by System/34. On
a 4-wire nonswitched line, , RTS' can be switched by
System/34, held permanently on by System/34, or held
permanently on by the modem. On a switched line,
'RTS' is switched by System/34. The 'RTS' line is on
during the transmission of each block or frame.
The 'standby' line selects the switched network backup
(SNBU) line.
The 'test' line selects the modem wrap function. When
the modem wrap test is running, the transmit function
of the modem is sent back to the receive function of the
modem.
805
..
J07 Test (wrap)
804
..
J06 Rate Select
-
The ' DTR' (data terminal ready) line signals the modem
that the terminal is ready to send or receive data. On a
switched line, 'DTR' initializes and holds the line
connection.
The 'rate select' line selects the bit rate on modems
with half speed. When this line is down, half speed is
selected.
The ' CTS' (clear to send) line indicates that the modem
is ready to transmit data. On a 4-wire nonswitched line,
'CTS' can be active all the time. On a 2-wire
nonswitched or switched line, , CTS' is turned on and off
by the ' RTS' line.
The' DSR' (data set ready) line indicates that the modem
is ready. The modem is ready when power is on, when
the modem is connected to the line, and when the
modem is not in test mode; all three conditions must be
met.
The 'ring indicator' line indicates that the modem is
receiving a call.
18
..
-
23
..
-
802 J02 DTR (data terminal ready) 20
.
002
004
B03
809
Adapter
..
810
..
013
...
..
808
-
813
--
....
807
..
...
012
..
008
Line 1 A-83F2
Line 2 A-83G2
Line 3 A-83H2
Line 4 A-83J2
-
.
..
..
...
G03
G07
G05
G08
EIA/
CCITT
__ G04
Interface
... G10
--
Card
.. J10
.. J09
.... J04
--
- G13
..
...
J08
Line 1 A-83L2
Line 2
A-83M2
Line 3 A-83 L4
Line 4 A-83M4
*New Sync requires a ooara jumper
RTS (request to send)
Transmit Data
Standby
New Sync*
Receive Data
CTS (clear to send)
Receive Timing
DSR (data set ready)
Transmit Timing
R I (ring indicator)
Signal Ground
Pin numbers of
the RS232/CCITT
connector
Figure 30-26. Modem Control Lines for EIA/CCI". Interface
~
30-660
4
2
11
14
3
5
17
6
15
22
7
.
-
--.
-
Modem
Note: The cable wra p connector connects the
testing: following signals for
DTR to DSR
RTSto RI
Transmit Data to CTS
Rate Select to Transmit Timing
Wrap to Receive Data
Standby to Receive Timing
Multiline Communications Adapter 43
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