Before you build your own development kit (talk about reinventing the wheel!) you will want to buy one.

This way you will be able to develop the test programs that will be necessary to verify the new hardware you've built...otherwise when something doesn't work you will have a chance to figure out what's wrong, especially if you don't have a lot of tools (DSO, etc.).

You know, when you first power it up, it will just sit there and do absolutely nothing... What is wrong? Hardware? Software? Programming of the uC?

Save yourself some headaches!

Then you need to decide whether you want to develop 8051 hardware or software. Which ever you choose it really helps if the other is known good and rock solid stable.

Dennis