"what hardware do I need to program the P89C51RD2?"
NONE, except for your board with the RS-232 port you will want anyhow. You must tie !EA/Vpp DIRECTLY (no resistor) to +5V but since you have all 64k of code memory inside the chip, you will want that pin high anyhow, so just make that a permanent feature, not a "programming mode switch". To program, you must have your application code "write to status register" as described in http://www.semiconductors.com/acrobat/a...N461_7.pdf then reset (power off) then use FlashMagic (free from esacademy.com) to program your chip, and after a reset your updated application will be running (if it can :-). Now, how do you get your application loaded until you have the code to set the status register - easy - two clip leads: PSEN to ground and ALE to Vcc through a resistor, reset the uC, remove the clip leads, use FlashMagic as above. If you are not using ALE (internal memory only) you can skip the cliplead on ALE, just let the pin float (which it should anyhow if you are not using external memory). One small requirement: if you use P2.7 and P2.6 as inputs, your circuit must be such that they are not held low during and after reset (till your appcode runs), this part of AN-461 may be confusing, 1) it only stets bit 7, it is bit 7 and bit 6: 2) it says "must be 1", this is already the case in your circuit unless you use them as inputs.

Hope this and AN-461 clears it up.

Have fun,

Erik

PS if you insist, you can, of course, use a switch or pushbutton instead of the clipleads, but since it becomes superfluous after you have got the first part of you app running, why waste time and money.

EM