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2-6 Modem 3600
Telephone Line Connection
The modem operates in these line-related modes:
• Dial
• Leased
20 CD 108.2 Data
Termi-
nal
Ready
This circuit is positive when the
DTE is ready to originate or
answer a call in dial-up operation.
DTR must always be active (high)
in 2-wire private line operation.
Cycling DTR causes retraining.*
21 -- 140 Remote
Digital
Loop-
back
A positive level causes a digital
loopback test mode at the remote
modem.*
22 CE 125 Ring
Indicator
In direct dial operation this circuit
is positive in response to an
incoming ring signal.*
23 CH 111 Data
Rate
Select
Supplies a data rate control input
to select primary or fallback data
rate: Negative voltage selects
primary data rate and positive
voltage selects fallback data rate.*
24 DA 113 External
Trans-
mit
Clock
A serial data rate clock input from
the data source. Positive clock
transitions correspond to data
transitions.
25 -- 142 Test
Mode
Indicates the modem is in a test
mode.
Table 2-1. Pin Signal Descriptions (Continued)
Pin
EIA-
232D
CCITT
V.24 Signal Description
*
* Modem options may force these signals on or cause them to be ignored.
*
** Refer to Appendix C, Hardware Options.
*
† This function can be disabled or its logic sense reversed by hardware straps.