Aaron:
The Silicon Labs parts are 3.3 volt surface mounted parts with on-board flash. Some parts permit external memory for data but none support external memory for code execution by the 8051 CPU core.

In the case of the 'F220 ... I would look at the 'F226 instead. It has an additional 1K of SRAM over the 'F200. Note that the 'F2xx parts do not have external bus support for additional RAM.

Michael Karas