Using a box of old X-10 stuff
I started using the CM11 and the RR501, among other X10 components back in the 90's, and I still use them. (I first used X10 in the late 70's). One warning I need to make: X10 has become less and less reliable with the advent of switching power-supplies. When X10 first came out, home power was pretty quiet, but today there is a lot of noise from switching on the AC line that often swamps the X10 signal. I've bought a number of LED light bulbs recently that have completely disabled my X10 network when I turned them on. Part of the problem with the X10 protocol is that the commands are sent out blind - no acknowledgements. So if a command gets lost, it's lost for good, and things simply don't work. This applies to both the power-line X10 and RF X10 protocols. Now on to the meat.

The CM11A:

I have the programming manual for the CM11A, try googling "CM11A Serial Interface Protocol.txt". The protocol is overly complicated for what it needs to do, and I have not found a USB to serial convertor that it works with (but it's been a few years since I looked). I use it from a standard RS232 port on an old PC. I also have the schematic and someone's rewrite of its firmware (PIC16C58), but I doubt that either of those would be useful to you.

The CM11A has a built-in clock and an internal EEProm. Commands can be pre-loaded to be run a specific times, so it works well as a standalone controller. I don't use it that way.

The RR501:

The RR501 is both an appliance controller (no dimming) and a RF to power-line bridge. The RF portion of X10 uses an ASK modulated 310MHZ signal that the RR510 can receive. It then repeats the received command in the power-line protocol, to either control a device directly or to inform the CM11A. But although the CM11A can handle all housecodes, the RR501 only handles the one that you set. If you have any of the RF X10 motion sensors or keychain remotes, the RR501 is a necessary ingredient to get those RF commands onto the power-line.

If you have any problems finding the documentation, let me know, and we can figure out how to get what I have to you.