Grounding GPIO pins during 8051 programming
I strongly suggest that you take the antique AT89C2051's to the trash can and then head over to www.silabs.com and take a close look at their 8051 clone lineup. These parts are way better and you can get USB programming pods for about 20 bucks which is way better than you can do trying to hack your own. Another huge benefit is that the same USB pod can be used to interface with the full debug support built into each chip that allows run/stop operation, data and code breakpoints, viewing registers memory and peripheral registers.