RabbitCore RCM3900
User's Manual
PREV INDEX NEXT

6. Using the TCP/IP Features

6.1 TCP/IP Connections

Programming and development can be done with the RCM3900 modules without connecting the Ethernet port to a network. However, if you will be running the sample programs that use the Ethernet capability or will be doing Ethernet-enabled development, you should connect the RCM3900 module's Ethernet port at this time.

Before proceeding you will need to have the following items.

A Cat. 5 straight-through and a Cat. 5 crossover Ethernet cable are included in the RCM3900 Development Kit. Figure 11 shows how to identify the two cables based on the wires in the transparent RJ-45 connectors.


Figure 11. How to Identify Straight-Through and Crossover Ethernet Cables

Ethernet cables and a 10Base-T Ethernet hub are available in a TCP/IP tool kit. More information is available at www.rabbit.com.

Now you should be able to make your connections.

  1. Connect the AC adapter and the programming cable as shown in Chapter 2, "Getting Started."

  2. Ethernet Connections

    There are four options for connecting the RCM3900 module to a network for development and runtime purposes. The first two options permit total freedom of action in selecting network addresses and use of the "network," as no action can interfere with other users. We recommend one of these options for initial development.

  3. No LAN — The simplest alternative for desktop development. Connect the RCM3900 module's Ethernet port directly to the PC's network interface card using either a Cat. 5 crossover cable or a Cat. 5 straight-through cable.

  4. Micro-LAN — Another simple alternative for desktop development. Use a small Ethernet 10Base-T hub and connect both the PC's network interface card and the RCM3900 module's Ethernet port to it using standard network cables.

    The following options require more care in address selection and testing actions, as conflicts with other users, servers and systems can occur:

  5. LAN — Connect the RCM3900 module's Ethernet port to an existing LAN, preferably one to which the development PC is already connected. You will need to obtain IP addressing information from your network administrator.

  6. WAN — The RCM3900 is capable of direct connection to the Internet and other Wide Area Networks, but exceptional care should be used with IP address -settings and all network-related programming and development. We recommend that development and debugging be done on a local -network before connecting a RabbitCore -system to the Internet.

The PC running Dynamic C does not need to be the PC with the Ethernet card.

NOTE Checking and debugging the initial setup on a micro-LAN is recommended before connecting the system to a LAN or WAN.

  1. Apply Power

    Plug in the AC adapter. The RCM3900 module and Prototyping Board are now ready to be used.

6.2 TCP/IP Primer on IP Addresses

Obtaining IP addresses to interact over an existing, operating, network can involve a number of complications, and must usually be done with cooperation from your ISP and/or network systems administrator. For this reason, it is suggested that the user begin instead by using a direct connection between a PC and the RCM3900.

In order to set up this direct connection, you will have to use a PC without networking, or disconnect a PC from the corporate network, or install a second Ethernet adapter and set up a separate private network attached to the second Ethernet adapter. Disconnecting your PC from the corporate network may be easy or nearly impossible, depending on how it is set up. If your PC boots from the network or is dependent on the network for some or all of its disks, then it probably should not be disconnected. If a second Ethernet adapter is used, be aware that Windows TCP/IP will send messages to one adapter or the other, depending on the IP address and the binding order in Microsoft products. Thus you should have different ranges of IP addresses on your private network from those used on the corporate network. If both networks service the same IP address, then Windows may send a packet intended for your private network to the corporate network. A similar situation will take place if you use a dial-up line to send a packet to the Internet. Windows may try to send it via the local Ethernet network if it is also valid for that network.

The following IP addresses are set aside for local networks and are not allowed on the Internet: 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.255, and 192.168.0.0 to 192.168.255.255.

The RCM3900 uses a 10/100-compatible Ethernet connection. The RJ-45 connectors are similar to U.S. style telephone connectors, except they are larger and have 8 contacts.

An alternative to the direct connection is a connection using a hub. The hub relays packets received on any port to all of the ports on the hub. Hubs are low in cost and are readily available. The RCM3900 uses 10/100 Mbps Ethernet, so the hub or Ethernet adapter should be a 10/100 Mbps unit.

In a corporate setting where the Internet is brought in via a high-speed line, there are typically machines between the outside Internet and the internal network. These machines include a combination of proxy servers and firewalls that filter and multiplex Internet traffic. In the configuration below, the RCM3900 could be given a fixed address so any of the computers on the local network would be able to contact it. It may be possible to configure the firewall or proxy server to allow hosts on the Internet to directly contact the controller, but it would probably be easier to place the controller directly on the external network outside of the firewall. This avoids some configuration complications by sacrificing some security.


If your system administrator can give you an Ethernet cable along with the network IP address, the netmask and the gateway address, then you may be able to run the sample programs without having to setup a direct connection between your computer and the RCM3900. You will also need the IP address of the nameserver, the name or IP address of your mail server, and your domain name for some of the sample programs.

6.2.1 IP Addresses Explained

IP (Internet Protocol) addresses are expressed as 4 decimal numbers separated by periods, for example:

216.103.126.155

10.1.1.6

Each decimal number must be between 0 and 255. The total IP address is a 32-bit number consisting of the 4 bytes expressed as shown above. A local network uses a group of adjacent IP addresses. There are always 2N IP addresses in a local network. The netmask (also called subnet mask) determines how many IP addresses belong to the local network. The netmask is also a 32-bit address expressed in the same form as the IP address. An example netmask is:

255.255.255.0

This netmask has 8 zero bits in the least significant portion, and this means that 28 addresses are a part of the local network. Applied to the IP address above (216.103.126.155), this netmask would indicate that the following IP addresses belong to the local network:

216.103.126.0

216.103.126.1

216.103.126.2

etc.

216.103.126.254

216.103.126.255

The lowest and highest address are reserved for special purposes. The lowest address (216.102.126.0) is used to identify the local network. The highest address (216.102.126.255) is used as a broadcast address. Usually one other address is used for the address of the gateway out of the network. This leaves 256 - 3 = 253 available IP addresses for the example given.

6.2.2 How IP Addresses are Used

The actual hardware connection via an Ethernet uses Ethernet adapter addresses (also called MAC addresses). These are 48-bit addresses and are unique for every Ethernet adapter manufactured. In order to send a packet to another computer, given the IP address of the other computer, it is first determined if the packet needs to be sent directly to the other computer or to the gateway. In either case, there is an Ethernet address on the local network to which the packet must be sent. A table is maintained to allow the protocol driver to determine the MAC address corresponding to a particular IP address. If the table is empty, the MAC address is determined by sending an Ethernet broadcast packet to all devices on the local network asking the device with the desired IP address to answer with its MAC address. In this way, the table entry can be filled in. If no device answers, then the device is nonexistent or inoperative, and the packet cannot be sent.

Some IP address ranges are reserved for use on internal networks, and can be allocated freely as long as no two internal hosts have the same IP address. These internal IP addresses are not routed to the Internet, and any internal hosts using one of these reserved IP addresses cannot communicate on the external Internet without being connected to a host that has a valid Internet IP address. The host would either translate the data, or it would act as a proxy.

Each RCM3900 RabbitCore module has its own unique MAC address, which consists of the prefix 0090C2 followed by a code that is unique to each RCM3900 module. For example, a MAC address might be 0090C2C002C0.

TIP You can always obtain the MAC address on your board by running the sample program DISPLAY_MAC.C from the SAMPLES\TCPIP folder.

6.2.3 Dynamically Assigned Internet Addresses

In many instances, devices on a network do not have fixed IP addresses. This is the case when, for example, you are assigned an IP address dynamically by your dial-up Internet service provider (ISP) or when you have a device that provides your IP addresses using the Dynamic Host Configuration Protocol (DHCP). The RCM3900 modules can use such IP addresses to send and receive packets on the Internet, but you must take into account that this IP address may only be valid for the duration of the call or for a period of time, and could be a private IP address that is not directly accessible to others on the Internet. These addresses can be used to perform some Internet tasks such as sending e-mail or browsing the Web, but it is more difficult to participate in conversations that originate elsewhere on the Internet. If you want to find out this dynamically assigned IP address, under Windows 98 you can run the winipcfg program while you are connected and look at the interface used to connect to the Internet.

Many networks use IP addresses that are assigned using DHCP. When your computer comes up, and periodically after that, it requests its networking information from a DHCP server. The DHCP server may try to give you the same address each time, but a fixed IP address is usually not guaranteed.

If you are not concerned about accessing the RCM3900 from the Internet, you can place the RCM3900 on the internal network using an IP address assigned either statically or through DHCP.

6.3 Placing Your Device on the Network

In many corporate settings, users are isolated from the Internet by a firewall and/or a proxy server. These devices attempt to secure the company from unauthorized network traffic, and usually work by disallowing traffic that did not originate from inside the network. If you want users on the Internet to communicate with your RCM3900, you have several options. You can either place the RCM3900 directly on the Internet with a real Internet address or place it behind the firewall. If you place the RCM3900 behind the firewall, you need to configure the firewall to translate and forward packets from the Internet to the RCM3900.

6.4 Running TCP/IP Sample Programs

We have provided a number of sample programs demonstrating various uses of TCP/IP for networking embedded systems. These programs require you to connect your PC and the RCM3900 board together on the same network. This network can be a local private network (preferred for initial experimentation and debugging), or a connection via the Internet.


6.4.1 How to Set IP Addresses in the Sample Programs

With the introduction of Dynamic C 7.30 we have taken steps to make it easier to run many of our sample programs. You will see a TCPCONFIG macro. This macro tells Dynamic C to select your configuration from a list of default configurations. You will have three choices when you encounter a sample program with the TCPCONFIG macro.

  1. You can replace the TCPCONFIG macro with individual MY_IP_ADDRESS, MY_NETMASK, MY_GATEWAY, and MY_NAMESERVER macros in each program.

  2. You can leave TCPCONFIG at the usual default of 1, which will set the IP configurations to 10.10.6.100, the netmask to 255.255.255.0, and the nameserver and gateway to 10.10.6.1. If you would like to change the default values, for example, to use an IP address of 10.1.1.2 for the RCM3900 board, and 10.1.1.1 for your PC, you can edit the values in the section that directly follows the "General Configuration" comment in the TCP_CONFIG.LIB library. You will find this library in the LIB\TCPIP directory.

  3. You can create a CUSTOM_CONFIG.LIB library and use a TCPCONFIG value greater than 100. Instructions for doing this are at the beginning of the TCP_CONFIG.LIB library in the LIB\TCPIP directory.

There are some other "standard" configurations for TCPCONFIG that let you select different features such as DHCP. Their values are documented at the top of the TCP_CONFIG.LIB library in the LIB\TCPIP directory. More information is available in the Dynamic C TCP/IP User's Manual.

6.4.2 How to Set Up your Computer for Direct Connect

Follow these instructions to set up your PC or notebook. Check with your administrator if you are unable to change the settings as described here since you may need administrator privileges. The instructions are specifically for Windows 2000, but the interface is similar for other versions of Windows.

TIP If you are using a PC that is already on a network, you will disconnect the PC from that network to run these sample programs. Write down the existing settings before changing them to facilitate restoring them when you are finished with the sample programs and reconnect your PC to the network.

  1. Go to the control panel (Start > Settings > Control Panel), and then double-click the Network icon.

  2. Select the network interface card used for the Ethernet interface you intend to use (e.g., TCP/IP Xircom Credit Card Network Adapter) and click on the "Properties" button. Depending on which version of Windows your PC is running, you may have to select the "Local Area Connection" first, and then click on the "Properties" button to bring up the Ethernet interface dialog. Then "Configure" your interface card for a "10Base-T Half-Duplex" or an "Auto-Negotiation" connection on the "Advanced" tab.

NOTE Your network interface card will likely have a different name.

  1. Now select the IP Address tab, and check Specify an IP Address, or select TCP/IP and click on "Properties" to assign an IP address to your computer (this will disable "obtain an IP address automatically"):

    IP Address : 10.10.6.101

    Netmask : 255.255.255.0

    Default gateway : 10.10.6.1

  2. Click <OK> or <Close> to exit the various dialog boxes.

6.5 Run the PINGME.C Sample Program

Connect a Cat. 5 Ethernet cable from your computer's Ethernet port to the RCM3900 board's RJ-45 Ethernet connector. Open this sample program from the SAMPLES\TCPIP\ICMP folder, compile the program, and start it running under Dynamic C. When the program starts running, the green LNK/ACT light on the RCM3900 module should be on to indicate an Ethernet connection is made. (Note: If the LNK/ACT light does not light and you are using a hub, check that the power is not off on the hub.)

The next step is to ping the board from your PC. This can be done by bringing up the MS-DOS window and running the pingme program:

or by Start > Run

and typing the entry

Notice that the green LNK/ACT light flashes on the RCM3900 module while the ping is taking place, and indicates the transfer of data. The ping routine will ping the board four times and write a summary message on the screen describing the operation.

6.6 Running Additional Sample Programs With Direct Connect

The sample programs discussed here are in the Dynamic C SAMPLES\RCM3900\TCPIP\ folder.

The program BROWSELED.C demonstrates how to make the RCM3900 board be a Web server. Two "LEDs" are created on the Web page, along with two buttons to toggle them. Users can change the status of the lights from the Web browser. The LEDs on the Prototyping Board match the ones on the Web page. As long as you have not modified the TCPCONFIG 1 macro in the sample program, enter the following server address in your Web browser to bring up the Web page served by the sample program.

http://10.10.6.100.

Otherwise use the TCP/IP settings you entered in the TCP_CONFIG.LIB library.

The optional LCD/keypad module (see Appendix C) must be plugged in to the RCM3900 Prototyping Board when using this sample program. The sample program MBOXDEMO.C implements a Web server that allows e-mail messages to be entered and then shown on the LCD/keypad module. The keypad allows the user to scroll within messages, flip to other e-mails, mark messages as read, and delete e-mails. When a new e-mail arrives, an LED (on the Prototyping Board and LCD/keypad module) turns on, then turns back off once the message has been marked as read. A log of all e-mail actions is kept, and can be displayed in the Web browser. All current e-mails can also be read with the Web browser.

The sample program PINGLED.C demonstrates ICMP by pinging a remote host. It will flash LEDs DS1 and DS2 on the Prototyping Board when a ping is sent and received.

The sample program SMTP.C allows you to send an e-mail when a switch on the Prototyping Board is pressed. Follow the instructions included with the sample program. LED DS1 on the Prototyping Board will light up when sending e-mail. Note that pin PB7 is connected to both switch S2 and to the external I/O bus on the Prototyping Board, and so switch S2 should not be used with Ethernet operations.

6.6.1 RabbitWeb Sample Programs

The sample programs can be found in the SAMPLES\RCM3900\TCPIP\RABBITWEB folder.

6.7 Where Do I Go From Here?

NOTE If you purchased your RCM3900 through a distributor or through a Rabbit partner, contact the distributor or partner first for technical support.

If there are any problems at this point:

If the sample programs ran fine, you are now ready to go on.

Additional sample programs are described in the Dynamic C TCP/IP User's Manual.

Please refer to the Dynamic C TCP/IP User's Manual to develop your own applications. An Introduction to TCP/IP provides background information on TCP/IP, and is available on the CD and on our Web site.

Rabbit—A Digi International Brand
www.rabbit.com
PREV INDEX NEXT