Technical data

PortServer Terminal Server Page 109
Connecting Modems
Modems are generally equipped with DB-25 connectors, so it is usually necessary to buy or build
an adapter such as the ones mentioned previously. Since the modem control lines, RI (Ring
Indicator) and DCD (Data Carrier Detect) are on pins 1 and 10, respectively, of Digi’sRJ-45
jack, the adapter cable provided by Digi is ideal, since it has a 10-pin RJ-45 plug, and is
terminated in a modem-ready, DTE-configured DB-25 plug.
Altpin
If you want to use 8-pin RJ-45 to DB-25 adapters, a software feature called ALTPIN has been
incorporated into the PortServer software to swap the DCD and DSR signals. This makes DCD
available on pin 1 of an 8-pin RJ-45 connector.
RJ-45 ALTPIN WIRING: 8 PIN PLUG TO 10 PIN JACK
RJ-45 - 8 Pin Plug RJ-45 - 10 Pin Jack
RI
DCD*
RTS
GND
TxD
RxD
SG
CTS
DTR
DSR*
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
DCD
RTS
GND
TxD
RxD
SG
CTS
DTR
1.
2.
3.
4.
5.
6.
7.
8.
Pin 1
Pin 8
Pin 1
Pin 10
N/C
N/C
*Note that DCD and DSR have been swapped.
Digi device drivers do not require DSR in modem-control applications, and since almost all of
today s modems have auto-answering capability, the Ring Indicator signal is generally
unnecessary.
Note that to use Altpin, you must also configure the PortServer port for Altpin; see set flow
altpin on page 46.