Modem and Null-Modem Cables

This section describes the modem and null-modem cables available from Eicon Networks and how to use them. It also includes diagrams showing the pin-out wiring and signals for each cable, as well as instructions for making null-modem connections between two systems.

Connecting Two Workstations

This section describes how to connect two Linux servers, each with an Eiconcard, back-to-back using a null-modem cable. Depending on the types of Eiconcards you are linking, cable requirements vary. Match the correct cable to the Eiconcards you want to link.

Which Cables to Use?

The table below shows which null-modem cables to use to connect specific kinds of interfaces.

Eiconcard	Interface	Target Eiconcard	Cable
C-Class	V.24 (RS-232-C)	C-Class	V.24 Null-Modem Cable
S-Class	V.24 or V.35	S-Class	V.24/V.35 HSI/HSI Null-Modem Cable
S-Class	X.21	S-Class	X.21 HSI Null-Modem Cable
C-Class	V.24	S-Class	V.24 HSI Modem Cable, with the HSI Null-Modem Conversion Cable

For further information on cable diagrams and part numbers, see the respective sections on Modem and Null-Modem Cables in this section. Remember that not all cables are symmetrical: both ends of a cable are not necessarily identical.

Establishing Contact

The diagram below summarizes the proper configuration of hardware and software for a null-modem connection.

To make a back-to-back X.25/HDLC connection using a null-modem cable, follow these steps:

1.	Connect Server A to Server B using a null-modem cable. It does not matter which computer you select as A or B.
	Note: Make sure that the packet size, window size, and the number of VCs match on both ends. This can be verified by running eiconcfg and selecting the Eiconcard Services Protocol Configuration on Servers A and B. Match the X.25 and HDLC configuration values on the two gateways.
2.	On Server A, run eiconcfg and select Eiconcard Services Protocol Configuration.
3.	Go to the Sync Driver Configuration Screen and set Clocking to Internal.
	Note: When using an X.21 HSI Null-Modem Cable (300-032) to connect two Eiconcards, be sure to set both ends to NRZI encoding, Internal+DPLL, and the line speed to 19.2 kbps or less.
4.	Go to the HDLC Configuration Screen and set DTE/DCE Addressing to DCE.
5.	Save the changes you have made and exit eiconcfg.
	Note: You must reload the Eiconcard for any changes you have made in eiconcfg to take effect.
6.	On Server B, run eiconcfg and select Eiconcard Services Protocol Configuration.
7.	Go to the Sync Driver Configuration Screen and set Clocking to External.
8.	Go to the HDLC Configuration Screen and set DTE/DCE Addressing to DTE.
9.	Save the changes you have made and exit eiconcfg.
	Note: You must reload the Eiconcard for any changes you have made in eiconcfg to take effect.
	Note: If you receive the error message "Modem Not Ready," then you may have the two ends of the null-modem cable reversed. Unplug the cable and reverse the ends. This error may also be caused by a damaged cable.

Modem Cables

This section contains information, including pin-out diagrams, on all Eicon Networks modem cables.

All current modem cables for Eiconcards are shown in the table below. These cables may be ordered from your Eicon Networks distributor.

Cable Name	Part Number
V.24 Modem Cable	300-007
V.35 HSI Modem Cable	300-024
X.21 HSI Modem Cable	300-025
V.24 HSI Modem Cable	300-026
HSI/V.24 Converter	300-046

Note: Not all cables are symmetrical: both ends of a cable are not necessarily identical.

These modem cables can be used to perform the following functions:

	The V.24 Modem Cable connects an Eiconcard with a V.24 (RS-232-C) interface to a modem.
	The V.35 HSI Modem Cable connects an Eiconcard with a high speed interface to a V.35 modem.
	The X.21 HSI Modem Cable connects an Eiconcard with a high speed interface to an X.21 modem.
	The V.24 HSI Modem Cable connects an Eiconcard with a high speed interface to a V.24 modem.
	The HSI/V.24 Converter makes an HSI port look like a regular V.24 port.

All connectors specified in the following diagrams must have a shielded ground. Small boxes around the wires denote a twisted pair. For complete wiring diagrams, contact your Eicon Networks representative.

Note: The V.24 Modem Cable, the V.24 HSI Modem Cable, and the HSI/V.24 Converter are fully symmetrical.

Null-Modem Cables

This section contains information, including pin-out diagrams, on various Eicon Networks null-modem cables, .

All current null-modem cables for Eiconcards are shown in the table below. These cables may be ordered from your Eicon Networks distributor.

Cable Name	Part Number
V.24 Null-Modem Cable	300-022
V.24/V.35 HSI/HSI Null-Modem Cable	300-031
X.21 HSI Null-Modem Cable	300-032
HSI Null-Modem Conversion Cable	300-033

Note: Not all cables are symmetrical: both ends of a cable are not necessarily identical.

These null-modem cables can be used to perform the following functions:

	The V.24 Null-Modem Cable connects an Eiconcard to another Eiconcard, using an V.24 interface.
	The V.24/V.35 HSI/HSI Null-Modem Cable connects an Eiconcard HSI to another Eiconcard HSI, using a V.24 or V.35 interface.
	The X.21 HSI Null-Modem Cable connects an Eiconcard HSI to another Eiconcard HSI, using an X.21 interface. When using this cable to connect two Eiconcards, be sure to set both ends to NRZI encoding, Internal Clocking, and the line speed to 19.2 kbps or less.
	The HSI Null-Modem Conversion Cable connects an Eiconcard HSI to a HSI Modem Cable connector.

All connectors specified in the following diagram must have shielded ground. Small boxes around the wires denote a twisted pair. For complete wiring diagrams, contact your Eicon Networks representative.