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Getting Started with an SPE

This document is intended to help new users get up and running with a Harvest Serial Port Extender (SPE). The idea is to set up the network and an SPE, simulate a remote device by sending serial data, and then have the SPE send that data back to your own computer via the GPRS network.

What You Need

  • A Harvest SPE with a power supply (5–30V DC for a standard SPE), antenna, and debug cable. This document assumes you have one of our newer g20/g24 SPEs, but an older g18 SPE will work just as well.
  • A SIM card. Usually you can get a SIM card from your GSM network operator. The SIM must have GPRS enabled and be set up with an internet APN (Access Point Name). Some providers can also set up private APNs—especially useful if you need static IP (internet protocol) addresses or more secure communication.
  • A PC with a serial port and a DE9 (9-pin D-connector) serial cable. Many desktop PCs have built-in RS-232 serial ports (e.g., COM1), but if not, you can easily use a USB-to-serial converter.
  • A terminal program, used to simulate a remote serial device, e.g., a data logger. Harvest's SPE-friendly terminal program works nicely, and it's available as an executable or a zip file. HyperTerminal, which comes with Windows, also works, but it's usually harder to set up and use.
  • Our UDPTerm program, available as an executable or a zip file. Among other things, UDPTerm displays the packetised data from the SPE, and allows you to talk back to the remote device (in our case, the terminal program).

Network Setup

  • Check IP data path. You need to make sure you have an IP data path from the internet (and therefore the SPE) back to your PC. The SPE communicates using UDP (User Datagram Protocol) and, by default, ports 7777 and 7778. Usually this is not a problem if you use a dial-up modem, but a broadband router or a larger company may have a firewall to block these ports. You'll either have to unblock these UDP ports or try to get your IT department to forward the ports through to your computer. Failing that, try using a dial-up modem.
  • Dial up. If you're using a dial-up modem or a VPN (Virtual Private Network with your own APN name), connect now.
  • Find your computer's IP. In Windows, you can get your computer's IP address by pulling up a command prompt (go to the Start menu, select Run, then type cmd) and typing ipconfig. Now read off the appropriate IP address. If you're using an external router, you'll have to find the router's IP address (which may change each time you connect). Or, if you're part of a company network, you'll have to ask your IT department what your external static IP address is.

SPE Setup

  • Insert the SIM card. On g24 SPEs, the SIM carrier next to the g24 module flips up to allow insertion. On g18 units you must slide the SIM under the g18 module, contacts-up, in the orientation outlined on the SPE board.
  • Connect the antenna. On most SPEs, the antenna connector is on the end opposite the green and red LEDs.
  • Connect the power. The power connector is located between the LEDs and the RS-232 serial connector. Just after you connect the power, both LEDs should light up for about five seconds.
  • Talk to the SPE. Run Harvest's terminal program. If you're using COM1 you can just double-click on terminal.exe. If not (say a USB-to-serial converter using COM4), you'll have to pull up a command prompt and type terminal COM4. Pressing Alt-H will send an SPE hangup sequence, ensuring you can send commands to it (see note below). You should soon see a string of characters including AT^HESC and ending with OK. Try typing AT^HSN to ask the SPE to give you its Harvest serial number. (Note that you must press Enter after each command. Successful commands respond with OK.)
  • Set the APN and remote IP. First set the SPE's APN name by typing AT^HAPN="name", where name is the name of your provider's internet APN, e.g., AT^HAPN="". Then set the remote IP by typing AT^HRIP="address",7777, where address is the IP address of your computer as above, e.g., AT^HRIP="",7777. If you receive OK after entering both commands, your SPE is ready to go.
  • Set username and password if needed. Some providers require a username and password with certain APNs. If you need them, use the AT^HUSER="username" and AT^HPASS="password" commands.

Note: If you're using another terminal program such as HyperTerminal, you'll have to set the baud rate to 9600, and you may have to enter the SPE escape sequence before you can talk to it. You do this by typing AT^HESC (all caps, no spaces).

Your First Call

  • Setup UDPTerm. Start udpterm.exe and go to Options menu and then Settings. The default settings should be fine, but check to make sure: Local IP address set to, "automatic remote IP and port numbers" boxes ticked, and local data and control ports set to 7777 and 7778, respectively. Note: If you have multiple network connections (like dial-up and local area network) you may need to set UDPTerm's local IP field to your computer's local IP address.
  • Make a call. Go back to the terminal program and type ATD499 to ask the SPE to connect to the GPRS network. You should see CONNECT almost immediately, and once it's connected, you should see COM, as well as the green light. If it doesn't work, you won't see COM and you might get a red light—check the SIM card, the antenna and coverage, and ensure the APN was set correctly above.
  • Send some data. Once you see COM, type any string, e.g., Hello world! The SPE should convert this string to IP packets and send them to your PC via the GPRS network. If all is well, you'll now see "Hello world!" appear in UDPTerm's Data Port window. If the data doesn't come through, check that you're connected to the internet and make sure your firewall isn't blocking port 7777. You might also check that the remote IP address was set correctly above.
  • Send data back. To send data back to the SPE, simply type something in UDPTerm's Data Port window. The data should go via the SPE to the "remote device", that is, it should appear in the terminal program. On most GPRS networks, you must not wait too long before sending data back (Vodafone New Zealand has a timeout of 60 seconds).
  • Try an SPE command remotely. Type AT^HVER in UDPTerm's Command Port window. Data typed here goes not through the SPE but to the SPE as a command. You should soon receive the SPE's software version and OK in response.

What Next?

Now that you have a basic SPE setup working, you'll want to tailor it to suit your needs. Here are some of the SPE commands you're likely to use:

  • AT^HBPS to set the bit rate and character format the SPE will use to talk to the serial device (the DTE).
  • AT^HPFC and AT^HPTO to tell the SPE how and when to assemble data from the DTE into packets.
  • AT^HPOC to get the SPE to automatically connect whenever DTR is asserted (e.g., whenever the DTE has data to send).
  • AT^HASE and AT^HAFS if you want to send a custom announcement whenever the SPE makes a call.
  • AT^HSCO and AT^HSCT to configure when the SPE will make calls.
  • AT^HLPM to turn on low power mode for battery-powered applications.
  • AT^HVER to read the SPE's software version, AT^HSN to read its Harvest serial number, AT^HSAS to show all its settings, or AT^HRST to reset all settings to their factory defaults.

For more information, see our other SPE technical information. If you get stuck, don't hesitate to contact us.


If at any point something doesn't work, you can often get more information from the SPE's debug port. This is the boxed three-pin connector next to the lithium coin cell. Simply connect the debug-to-DE9 cable we provide to a spare serial port on your PC (if you don't have a spare serial port, you'll have to use a USB-to-serial device). Then run another copy of your terminal program with the correct COM port at 9600 bps (e.g., terminal COM4).

Plug in the debug cable, run the terminal program, then power up the SPE. You should see a bunch of debugging messages when the SPE turns on as well as when it tries to connect.

Note: On older, g18 SPEs you'll need one of our programming adaptor boards, but you can use the terminal program in the same way.