252 • SMP Gateway User Manual
28.3.1 Physical Layer
The physical connection between the SMP Gateway and a device is often at the root of a problem.
You should therefore ask yourself the following questions:
Am I using the correct type of cable?
Do I need to use a cable for RS-232 or for RS-485 communications?
Should I be using a 2-wire or a 4-wire cable for RS-485 communications?
Is the device connected properly?
Make sure the cable is connected to the correct port.
Do I need an adaptor?
For example, do I need a null-modem adapter for RS-232 communications?
Are the TCP/IP network settings configured correctly?
Use SMP Config to check the Asynchronous Serial Ports settings, under Connections:
If I’m using RS-485 4-wire, did I choose RS-422?
If I’m using RS-485 2-wire, did I choose RS-485?
28.3.2 Link Layer
Problems in the link layer are often related to the settings of the communications component.
Here are examples of settings that can cause problems:
The baud rate, parity, start and stop bit settings of both the SMP Gateway and the device, for
serial communications.
The TCP/IP address and port configuration, for TCP/IP communications.
We suggest you take the following steps:
Examine the link layer byte exchanges, using SMP Trace and SMP Stats.
Using SMP Config, look at the Connections settings:
If your SMP Gateway communicates with the device over a serial link, check the
communications settings of the link used to communicate with the device, such as baud
rate and parity. These settings must be configured identically at both ends.
If your SMP Gateway communicates with the device over a WAN or LAN, make sure
you have specified the correct TCP/IP address and port number.
28.3.3 Protocol Layer
Protocol problems are directly related to the settings of the protocol instance used to
communicate with the device.
You should proceed as follows:
Verify the configured device address.
Verify the protocol version.
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