What is the smallest (size) PIC with internal oscillator available which the TCP/IP stack can be implemented (and used) successfully? Also, what is the smallest (size) PIC with internal oscillator and Ethernet stack implemented?
If you're going to use Microchip's TCP/IP Stack, the PIC18 is the 'lowest-end' family of PICs that the software stack supports.
- IEEE 802.3 compatible Ethernet Controller
- Fully Compatible with 10/100/1000Base-T networks
- Integrated MAC and 10BASE-T PHY
- Up to 128KB Flash
- 8 KB Ethernet Buffer
- Support for Unicast, Multicast and Broadcast packets
- Programmable wake-up on multiple packet formats,including Magic Packet®, Unicast, Multicast, Broadcast,specific packet match or any
- 64/80/100-Pin TQFP Package
You may want to explore the ENC28J60. It's an external chip from the PIC that handles all the Ethernet. It interfaces to the PIC via SPI bus. Just choose a PIC that has enough flash and RAM for the TCP/IP Stack. You can download and compile to a simulator to see how much space things take.
On the link provided by m.Alin you can see in the right bottom corner a button named
See all Ethernet PIC MCUs which lead to here where you can see different characteristics, including packaging in the most right column. By the look of it, the smallest PIC32 with Ethernet are 64/QFN 64/TQFP