8 posts and all talk about development board and 8051.
can you use Proteus to simulate MCU and 8051 in keil.
After a quick Google, I assume we're talking about this Proteus:
www.labcenter.co.uk/.../8051.htm
It's got a big Keil logo right on top of the web page, so I'm guessing it works. Keil is in their supported compilers list:
www.labcenter.co.uk/.../compilers.cfm
Proteus is an 8051 simulator, so it's their job to get the simulation right. The code produced by Keil tools should work fine as long as the simulator is accurate.
The Keil tools have their own simulator that handles a wide variety of parts. The advantage of Proteus is to simulate the rest of the board, outside the the MCU.