First, thanks for advertising the Codex! Right now, however, we don't have a way to directly post files, except through the discussion forums. however, the size we're talking about I think is too large for the forums upload system. I'll see if I can get a "white papers"-style upload system in place...

OK, there are a few issues here. First, the Stamp is only in the RC. The OI consists of several other types of ICs. Similarly, the RC is A LOT more than just the Stamp. There are also processors for input, output and a master processor to control it all. This master processor (or mater uP) is the only thing the Stamp communicates with directly.

As for what comes out of the computer, its sorta complicated. It starts by waiting for a 255,255,1 sequence, then reads the next 11 bytes. These eleven bytes contain all eight sensors, both bytes of rc switches, and a control byte that I use internally to prevent bytes from every being 0 (Windows doesn't like sending or receiving 0 as it thinks it is the end of the message). It then waits to get back a 255,255,255 sequence indicating that the Stamp is ready to receive the new data. It then sends a 20-byte packet to the RC that contains all 16PWMs, both relay bytes, a byte for all eight LEDs, and a control byte similar to the one I discussed previously.

If you want to see this as actual code, open up the "RoboCon RC.bsx" file and take a look.

Finally, do you have an OI and an RC and the necessary cables (one F-F and one M-F)? If so, I'll try to write a little program in the next few days to record everything that gets sent back-and-forth between the two.

As another note, would people be interested in a more detailed description (possibly even a whitepaper) on the overall setup of the RC and OI?

yes. Very much so. I had to teach myself everything i know about PBASIC and all of its associated what not. I know enough to get by, and I get most of it, but a few questions bother me, such as :

If the main stamp is on the RC, then how does the OI respond to it? Are the screamers bi-directional? I hooked up the modems in backwards for kicks once, and the RC got short spurts of signal. IE. Pause .5sec, lurch, pause, lurch.

I think i can get a serial port monitor up and running on my own, but i wouldnt mind if you did it. I tend to break things in my debuging attempts. I do have the cables required, i just need to find them and the rc&oi. It'll be fun.

The important thing to keep in mind is that the Stamp is a VERY small part of the OI/RC system. Basically, it is only there to allow us to program more easily. After all, a Stamp IIsx is only about $30-$45, but the whole RC/OI setup is $1145. There are SEVERAL other microprocessors that are far more expensive than the Stamp in both the RC and the OI. These are the ones that deal with all the communications between the two pieces.

As for the Radio Modems, they ARE bi-directional. After all, the OI needs to send Joystick data to the RC and the RC needs to send dashboard/LED data to the OI.

If you feel like doing the serial port thing yourself, I'd appreciate it as I'm currently in the middle of the Linux port of RoboEmu. About the only advice I can give you is that the Radio Modems are 9600bps, so I would guess the thether probably is too.

--Rob

This will probably end up being a long post, and hopefully I can answer a lot of questions from this thread. But before I do that, I need to stress one thing: DO NOT connect a computer directly to the tether port of either the OI or the RC! The tether port carries standard serial data, but it also has +12V on one of the pins (think about it: the OI gets power from the RC when in tether mode, so this power has to come from somewhere). If you hook this up to a computer, there is a good chance you will ruin either the serial port on the PC or the RC itself or both.

OK, now that that's out of the way... Myself and some other members of team 111 experimented a lot with this last season. We successfully built a miniature operator interface out of a Motorola HC08 microprocessor that talks directly to the RC over the tether port. So it definitely can be done. However, we also have a lot of fancy equipment here at Motorola that allowed us to figure it all out before we destroyed anything. If you don't know exactly what's on each pin of the tether port, then you shouldn't be hooking the RC up to anything other than the OI.

The OI is sending several "important" pieces of data to the RC, even in this case. One of the bytes in the datastream from the OI to the RC is your team number. The RC will not function unless it is receiving this team number in the stream. There's also 2 checksum bytes, an "enabled" bit, etc.

We've obviously figured out the whole bi-directional protocol since we can control the RC with our own software. Right now I'm thinking it's not a good idea for me to share the protocol as it will almost certainly just lead to lots of dead RCs from people trying to hook up to them. I can tell you this though: the RC-->OI data stream is the exact stream you get out of the Dashboard port. So if you read the spec for that you'll get a very good idea of what's going on between the OI and the RC. The reverse direction is extremely similar.

The screamers are indeed bidirectional. I'm a little surprised that hooking them up backwards didn't work. Functionally, the radios on each side of the link are identical, except for the Tx/Rx frequencies are opposite. If you want to learn more about the radio modems, visit www.electrowave.com and look for the SCREAMER422 technical manual.

It's been about 6 months since I looked at this, but if I recall correctly, there are 3 processors in the RC: Two PICs and the Stamp. The two PICs do the majority of the work, and run considerably faster than the Stamp. However, they are a lot cheaper. At $30-45, the BS2SX is easily one of the most expensive microcontrollers on the market. The PICs in the RC are probably between $5-10. The HC08 that we used in our Mini OI was $3. With the Stamp, you are paying a hefty price premium for the "ease of use" of the PBASIC language, though I'd argue that programming a regular microcontroller in assembly isn't really that much more difficult, and would be a lot more useful to students interested in computer science/engineering (but that's another topic altogether!).

So if the microcontrollers in the RC and OI are so cheap, why does it cost $1200, you ask? Well, I can't say for sure, but just guessing I'd say that it's because it's such a low volume product that they have to charge that much to recoup their costs in designing the hardware and writing the software to run it all.


Please let me know if you guys have questions about any of this. It's great to see so many people interested in the inner workings of the control system! This is exactly the kind of stuff that electrical/computer engineering is all about, and unfortunately I don't think either of these fields get enough exposure in the FIRST world.

Given that you hooked your HC08 up to the tether port, I assume you must have a pinout. If so, would you mind sharing that? If I knew which pin the +12V was on, I could merely disconnect that wire in the serial port and wouldn't have anything to worry about.

Also, would you mind sharing the HC08 setup, as this could be a fun project while we wait for Jan 4, and at $3 it would definately be one of the cheaper ones.