Post by thread:[EE]: [OT]: YAP-II / MAX-232 signal bunking.

I'm using a YAP-II board (which has a MAX-232 on it, I believe) and I have been trying to develop a simple project that talks to the PC via serial port. So, I have had a terrible time getting it to work reliably at > 2400 baud. I figured it might be my laptop serial port being crappy (though unlikely), I figured it could be serious calibration problem with the oscillator (again, unlikely). I tried debugging it "printf style" (ie turn LED on / off, and watch it on my scope) So, what it looked like was the bit period wasn't constant. Can't be, must be my cheeze ball scope, right? So, I bought another scope, this time wiht storage. Sure as hell the damn bit period is all whacked up. I put channel 1 on the "raw" input from the serial port, and channel 2 on the "SerOut" connector on the YAP-II board. For the most part the signals seem to agree on what a bit period is. However, every once in a while (every few bytes, maybe?) the signal coming from the YAP-II board is "squished" (that is, the bit period looks about 1/3 short) Any ideas what could be going on? Thanks... -Steve -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Hi Steve, The Serial Port (RS-232) Interface used with the YAP-II is a 3x sampling routine which nominally runs at 1200 bps. This means that once every 278 usecs, the YAP-II will be interrupted and the I/O line will be sampled/data output. By sampling every 278 usecs, the "middle" of an incoming 1200 bps data character (which has a 833.33 usec period) can be fairly accurately determined (from 33 to 67 percent of a bit period from the leading edge of the incoming data). The "pass through" feature (which it sounds like you are using) simply passes the data on the "Serial In" pin to the host computer during the interrupt handler (which takes place every 278 usecs as indicated above). It sounds like you are trying to pass 2400 bps data through the pass through interface. I would expect to see the occasionally "shortened" bit just as you indicated because sometimes the bit sampling would catch the "end" of a bit rather than the leading edge. Running the pass through interface at speeds other than 1200 bps was never allowed because the interface speed of the host computer would have to be changed while the PICmicro in the YAP-II was running AND at different speeds, it may be possible for the YAP-II to interpret a 0x003 ("Ctrl-C" or execution stop command character) from the different speed data coming in. When I am working on an RS-232 interface on a YAP, I use a second serial port with my PC rather than "tricking" the primary serial port connected to the YAP. In this case, I use a 2N3906 PNP voltage stealing RS-232 interface circuit or a DS275, both of which are very easy to wire on the YAP's breadboard. I don't know if this helps or confounds the problem. Drop me a line if you would like to talk about it some more. myke {Original Message removed}

I see now what is going wrong. It's not surprising, then, that 9600 baud didn't work at all :) I assumed that the YAP-II micro was just asserting a pin to turn on some passthrough switch from the MAX to the devel board. (all the while watching for the ctrl-c) So, now that I know the rest of the story, I can get on with my show. Thanks for your help. BTW: The YAP-II has been (almost) flawless in operation, and has helped me along quite a bit. Worth every penny. In particular the high quality components are appreciated. (ZIF socket, etc) (any chance the YAP-II can program a 12 series chip?) Thanks -Steve -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use spam_OUTlistservTakeThisOuTmitvma.mit.edu?body=SET%20PICList%20DIGEST

HI Steve, I'm glad I was able to help explain what was happening. And I'm glad it's working well for you. Yes, the YAP-II can do 8/14 pin parts - the changes I put in the instructions between it and the original (classic?) YAP allow programming 8/14 pin parts. To do this, I will have to update the YAP-II Windows Interface. I'll probably do that in a couple of weeks or so - I have been busy getting the final layout and CD-ROM ready for the second edition of "Programming and Customizing PICmicro(R) Microcontrollers". I'm hoping that I will have confirmation that it has gone to the printers by the end of next week. Good luck and let me know if you have any other questions about the YAP-II. myke {Original Message removed}

> Yes, the YAP-II can do 8/14 pin parts - the changes I put in the > instructions between it and the original (classic?) YAP allow programming > 8/14 pin parts. To do this, I will have to update the YAP-II Windows > Interface. Well, I don't use Windows (fortunately :), but instead dump straight to the serial port in linux. So, what will I have to do differently to get it to work for teh 8/14 pin parts? Thanks again for your help -Steve -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu