I understand that TCP/IP is useful for many applications, but I cannot find anything useful at all if you use IP over PPP or SLIP.

Please correct me if I'm wrong, but with PPP/SLIP you have point to point communication medium and to be able to connect large number of -your- embedded devices you have to use a kind of router, or something else.

Isn't this correct?

I looked a little to some of the free embedded TCPs with SLIP, and the only example was connecting the device to the serial port of a Linux machine. In this configuration, I think Linux is configured to forward packets between this serial interface and ethernet interface.

Based on these, if I do not have an Ethernet chip on board; TCP/IP seems useless to me. Because I can get all the features of using TCP/IP/SLIP-PPP by using a simple communication mechanism over RS232 and connecting the devices using a simple terminal server.

Terminal server acts as a gateway between multiple RS232 ports and an Ethernet interface. With this configuration, if the controller sends a byte -say 0x55- from RS232, it is received by the remote station (maybe a PC) as 0x55 over TCP over IP over Ethernet.

In this configuration, you do not waste your valuable RAM and ROM capacity for TCP/IP.

I'm not sure, but if you need web access to the device, implementing HTTP protocol over RS232 (instead of TCP) will be enough.

Am I completely wrong?