Serial RS232/NET232 Product FAQ

1. Why does your product not work with my device? I have a standard serial port!
2. What serial signals does the NET232 support?
3. Jumpers/Null Modem
4. Flow Control
5. Serial Tunneling
6. Redirector
7. I lost my static IP address/Reset
8. Web page configuration settings do not take effect.
9. NET232 Password Reset

Why does your product not work with my device? I have a standard serial port!

The first thing to know is that there is a serial standard but there is no such thing as a standard serial port.  The serial standard is a set of guidelines set forth by the Electronic Industries Alliance for serial communication. (www.eia.org)  In the specification are set forth physical and electrical characteristics such as what pin on a serial interface should carry what type of signal.   A serial port on a computer or device, although adhering to the serial standard, may not be using all of the signals set forth in the standard.  In fact, a device's serial port may be using only a portion of them, or may be varying in some other way from the standard.  With 1000's of serial products on the market, devices vary by manufacturer, type, and date brought to market.  A serial port on a very old device will likely be using different pin signals than a new device.  That being said, there are several common signals that you will find, namely:

Transmit (TX or TXD)
Receive (RX or RXD)
Ground (GND)
Request to Send (RTS) used for Flow Control
Clear to Send (CTS) used for Flow Control
DTR (Data Terminal Ready)
DSR (Data Set Ready)

In order for communication to take place between two serial devices, the pins on both devices and their corresponding signals must match.  The minimum required signals are TX, RX, and GND.  Without at least these three signals, communication will not take place.

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What serial signals does the NET232 support?

The NET232 supports TX, RX, RTS, CTS, and GND.  It does not support DTR, DSR, CD, RI by default, although customization may be possible depending on your needs.  Contact us and we'll discuss your situation with you.  We do carry other device servers such as the Netport* and UDS1100 that support these signals.

*The Netport is available on our FactoryComm Web Store.

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Jumpers/Null Modem

Jumpering as it applies to serial ports is a process of connecting two pins using a special jumper connector, or by wire or some other means.  Doing so completes a circuit between the two.   It is most often used to modify flow control requirements of a serial port. 

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Flow Control

Flow control is a way to control the flow of serial data from one device to another.  A sending device such as a computer is sometimes called a DTE (data terminal equipment) device.  A device attached to a computer such as a modem, is called a DCE (data communication equipment) device.  There are generally three types of flow control, hardware, software, and none.  Hardware flow control is accomplished on serial connections by the use of physical signals on serial port pins.  The different flow control signals are:

RTS - Ready to send/Request to Send
CTS -Clear to send
 

Often when using RTS/CTS flow control, a sending DTE device indicates that it is ready to send data by bringing up the RTS line.  The remote DCE device indicates its readiness to accept the data by responding with its CTS line signal positive.  If the flow of information to the remote DCE device becomes too fast for the device to handle, it takes back down the CTS line, and the sending device stops, waiting for the receiving device to process the data until it is ready again.

Software flow control controls the flow of information by the use of special characters in the actual data itself.  When a device sees an XOff character, this is an indication to stop the flow of information.  It can resume the flow of data when an XOn character is seen.  Flow control, however, is not used as much today.  Modern processors often operate fast enough that it is not necessary.

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Serial tunneling is a term describing how one more more serial devices can connect over a network, such as Ethernet, instead of through a serial cable.  It works by encapsulating serial data in ethernet packets and sending them over the network. This is one of the functions of the NET232.  It is transparent to the end devices, meaning that they function as if directly connected with a serial cable, even though they are traversing an Ethernet network.  By using tunneling, you can eliminate the distance limitations of a serial cable, in essence virtually extending it indefinitely.  There are two common ways in which serial tunneling is employed with the NET232. 

In this first picture, we see two NET232's used to connect a serial POS device over ethernet.  One net 232 is attached to the POS device, performing the encapsulation of serial data to send to the computer.  The NET232 attached to the computer is attached to the computer's serial port, so the data must be de-encapsulated by the NET232 back into serial data so the computer can receive it and understand it. The two NET232 A user in this case could connect to his remote device by connecting to COM 1 on his computer.  COM 1 is generally the term for your computer's physical serial port. 

In this picture, one NET232 is attached to the remote serial device.  The computer makes a TCP connection to the NET232, either from an application, telnet, or terminal emulator, and can then exchange data.  Most newer applications have the ability to make a TCP connection to a network host.  Legacy applications which can only connect to a COM port can use the redirector software included with the NET232.

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Redirector

The Com Port Redirector software distributed with our serial-to-ethernet products is a utility that gives your computer a virtual Com port.  This is useful when you are using software that does not allow connecting to an IP address.  The redirector software transparently redirects connections from your virtual Com port to an IP address, letting you connect to the NET232 from over ethernet, as if the attached serial device were locally attached to your physical Com port.

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I lost my static IP address/Reset

One of the ways of reassigning an IP address to the NET232 is with the included Device Installer software.  This is a utility to help you locate your NET232 on your ethernet network.  Upon hitting the search button, the software will return a list of all NET232's and Xport devices on your network.  Navigate to the appropriate device in the left hand tree and hit the assign IP button.  You will be given the choice of assigning a static IP to the device, or have the device request a DHCP address. You can check that you have located the appropriate device by comparing the MAC address listed in the utility to the printed MAC on the unit.  Devices in a different subnet than your computer will most often be listed in red.  You probably wont be able to communicate with the device.

In this case, or in case you have lost or forgotten a previously assigned IP, use the following method to assign a new IP to the device of your choosing, preferably one in the same subnet as the computer you are connecting from:

There is a method for resetting the IP address of our Lantronix based device servers, in the event the IP address was forgotten.  This is accomplished using ARP and Telnet.   First, create an entry in your PC's ARP table listing the intended new address of the unit, and the unit's MAC address, as follows:

arp -s 191.12.3.77 00:20:4a:xx:xx:xx

where 00:20:4a:xx:xx:xx is the MAC address of the unit, printed on the sticker, and the 191.12.3.77 is the intended new IP address of the unit.  Next, telnet to the new address on port 1 as follows:

telnet 191.12.3.77 1

The telnet connection will fail, but the device actually listens to the connection attempt, and recognizes it as a command to change its IP address to the new value temporarily.  Finally, open a telnet connection within three seconds to the same IP address on port 9999 and affirm the IP configuration. 

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Web page configuration settings do not take effect.

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NET232 Password Reset

To reset a password on the NET232, connect the serial port of the unit to the serial port of a computer. Open a terminal emulation program and make a terminal connection to your computer's serial port. The default settings for the NET232 are 9600,8,N,1, No flow control. If you have changed the default serial settings of the NET232, then you will have to set your terminal emulation program to match those settings instead. Power cycle the NET232, quickly hold down the "x" key on your keyboard. This will get you into configuration mode. You will see a prompt similar to:

MAC address: x.x.x.x
Software Version 6.5.0.7
Press enter for setup mode

Next, press enter within 5 seconds to get into setup mode. Choose option 0, "Server" Press enter to scroll through options under this category until you see the prompt: "Change telnet config password (N)?" Enter "Y" for yes. Then enter your desired new password. If you wish to not have a password simply leave this field blank, and hit enter. You will be taken back to the top level menu. Choose option 9 to save and exit.

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