Late night frustration and RS232 question

photomankc

Got the basic hardware today and spent the evening setting it using the diagram from the PE Labs kit but hit a major snag.· The PropPlug I got with it programed the device several times but·now it reports there is no chip found.· ID chip reports the same.· Several PC's all report the same.· The Prop is running it's code since I·loaded it in EEPROM too·but I can not program it anymore.· The PropPlug seems quite dead. I'm planning to call Parallax tomorrow to see about a replacement.· My real disappointment is I had several days of alone time to work with it and now I'm stuck with no interface.· Is there a simple fall-back to a serial cable that I could do?· I have an old MAX233 from a previous project but I'm a little leery if that is correct for handling the RS232 signals from the PC and the reset seems to be tied into the serial port too.· I could get the bits needed to put it together from the local Radio Shack if that MAX233 will work.

Is there any example schematic for an interface like that?



My other issue tonight·is that programs would run at 40Mhz but not at 80.· I think strapping the breadboard's metal base to ground may help with that since it also seemed to stop execution if that metal base was touched even at 40.· Now that it is strapped to ground·it has stopped doing it at 40 but I'm stuck since I can't test anymore now at 80.

Going to bed now.· Hope this makes sense to anyone.

Post Edited (photomankc) : 7/28/2009 8:50:56 PM GMT

Dr_Acula

Yes you can use an old max232. There is a standard circuit somewhere on this forum and in the help. I think it is replicated on the Pocketerm here http://www.brielcomputers.com/wik/images/0/01/PTschematic.pdf

Suffice to say the key is the transistor, two 10k resistors and a 0.01uF on the reset. And on the download part, you need two 1k resistors (R15/16) between the max232 and the Propeller. These provide a 5V to 3V interface. (or you could use a max3232 instead of a max232). The transistor is any small signal type, so you probably have enough bits lying around to get it working without needing to buy any more parts.

Vaati

I suggest you get a max3232e from ti.com You can get a sample and they ship in under 24 hours. I used one for a propstick kit, and it worked perfectly. Just make sure to get the DIP package.

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photomankc

I found the three transistor interface but I want to avoid spahgetti wiring on the breadboard. Transistors always make me feel like I'm playing electrical twister. Sounds like the MAX233 will work until I can get the new PropPlug. I can't find any electrical reason that it would have just poofed on me. I ordered some spare prop chips as well in case there is some other problem here. I've got enough other parts on hand to build the other chip out on another board to see if I get better results.


ETA: Does the prop expect the inverted signals of the drivers? I notice they all have inverters but I see no indication they need to be flipped back in the circuit using the MAX chips. Thanks for the pocket term schematic, that seems to be just what I'm looking for if a little hard to read.

Post Edited (photomankc) : 7/28/2009 3:03:15 PM GMT

dandreae

·Please give us a call at 1-888-997-8267 and ask for tech support.·
Thanks,
Dave


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Dave Andreae

Parallax Tech Support·

photomankc

I guess I will have a spare Prop Plug. In my late night fog I apparently moved a wire I did not recall moving. I had essentially cut off the reset from the Plug to the Prop Chip across the reset switch instead of tying them together and shorting them to ground when the switch was pressed. I looked I don't know how many times and didn't catch it. Duh moment there. I was just not remembering messing with that at all.

Testing is now going better. There is still a little weirdness in it with the 5Mhz crystall and pll16x. Sometimes, maybe 1 in 10 times the program loads but the chip never seems to start executing it. Loading it again will usually make it run though. It may just be something about this breadboard that's a problem. I have another breadboard and 2 more chips on the way so I should be able to build it out on them and see how that goes. It seems to run well at 64Mhz using an 8Mhz crystal and pll8x so that would at least get me a little better than the half speed offered by 5Mhz and pll8x. I'd rather a little slower and more reliable though I guess.