What are you trying to accomplish?

Is it just a "mental masturbation" project, or do you want to learn and experience something? If you want to learn, then what is it you want to learn? Do you know enough about basic electronics to get something meaningful done? Do you know how to solder or to wire-wrap a simple circuit? Do you already own the necessary equipment? What about test equipment? Do you have access to an oscilloscope, a multimeter, a frequency counter? How about a power supply?

Have you ever built a power supply? How did that turn out for you?

Do you know and understand about proper power supply bypass? Do you understand the consequences of improper or inadequate power supply design? Have you read the datasheets on a few of the 805x family members? Do you know the difference between read-write memory and read-only memory?

Have you ever programmed a computer or microcontroller?

If you scavenge a microcontroller that's more-or-less a "standard" 805x family member, it's likely it will have factory-programmed ROM as its internal program store. You won't be able to change that. That will limit you to using external EPROM/EEPROM/FLASH memory. Do you even know what those are? Do you have the means to program and to erase them?

If you're going to tinker with 805x family devices, it's likely you'll find it easier and less costly to use one of the popular serially programmable family members, of which there are many, though there are hardware requirements that you'll have to meet.

I'd advise you to focus on one or another of those serially programmable devices, to acquire a quiet, linear power supply so you don't have to fiddle with power supply design while you're fiddling with microcontroller circuit design, and decide whether you want to do all this badly enough to invest in the necessary test equipment to enable you to tell what you've done once you've done it.

You can buy a good "experienced" oscilloscope, a simple bench power supply, a multimeter, and a frequency counter for less than $1kUS, but are you prepared to do that? Without most of that equipment, plus the hardware necessary to construct a circuit, e.g. soldering and wire-wrap equipment, solder, flux, cleaning supplies, various passive components, prototype boards, etc, you'll find you're WAY better off with an evaluation kit of one sort or another, as offered by various manufacturers of 805x microcontrollers, and many of which have on-board programming hardware. Given a PC with a standard serial port, you can do a lot of playing with the chip in question without investing a "king's ransom." Of course, the oscilloscope, multimeter, and frequency counter will still help you to understand what you've accomplished, but you can get a lot done just by using one of those evaluation boards with a proper power supply and a PC serial port.

If you are really bent on reusing 805x's from scrapped circuit boards, or the like, that can be discussed in detail once you've considered these matters. I guarantee you, it's going to require lots of study, though.

Good luck in any case!

RE