Silicon Laboratories Network Card - Manual (Page 6)

E t h e r n e t - D K
6 Rev. 0.6
4.2. Selecting an IP Address for the Embedded System
For a PC to recognize an embedded system on a network, its IP address and subnet mask need to be configured.
Below are a few guidelines to follow when choosing an IP address for the embedded system. Figure 6 shows an
example of a compatible PC and embedded system IP address combination.
1. Find the IP address and Subnet mask for the PC. If a Default Gateway is specified, then save this address for
later use. If you are using a crossover cable, you may choose any IP address for your PC as long as the
Subnet mask allows it to recognize the embedded system.
2. The IP address chosen for the embedded system must match the PC’s IP address in all bit locations where
the Subnet mask is a 1 in order for the PC to recognize the embedded system. Otherwise, the PC will send
it’s request outside the local network.
3. Do not duplicate IP addresses or select a broadcast address. An IP address is considered a broadcast
address if all bits which are 0 in the Subnet mask are 1 in the IP address. Broadcast addresses with
additional 1s such as 10.10.255.255 (Figure 6) can be broadcast to nodes outside the local network.
4. The address 255.255.255.255 is known as the Ethernet broadcast address and is used when the Subnet
mask for the network is not known. Any packet transmitted to this address will reach all nodes on the local
network but cannot go further than the nearest router.
4.3. IP Address Selection Example
The example in Figure 6 shows the IP address and subnet mask of the PC we want to connect to the embedded
system. Since the first 24 bits of the subnet mask are 1, the first 24 bits of the embedded web server’s IP address
(shown in bold) must match the PC’s IP address. Only the least significant 8 bits may vary making the valid range
of IP addresses for the embedded web server 10.10.10.0 to 10.10.10.254 with the exception of 10.10.10.80 since
this address is already taken by the PC. 10.10.10.255 is reserved because it is the broadcast address for this
network.
Figure 6. IP Address Selection Example
PC IP Address
PC Subnet Mask
Embedded Web Server IP Address
0000 1010 0000 1010 0000 1010 0101 0000
10 10 10 80
1111 1111 1111 1111 1111 1111 0000 0000
255 255 255 0
(decimal)
(binary)
(decimal)
(binary)
0000 1010 0000 1010 0000 1010 1010 0011
10 10 10 163
(decimal)
(binary)