I have removed an earlier reply giving details of the circuit I had configured for the receiving unit as it was drawing more sarcasm than help. May I put things into perspective, I am 63 and stopped doing design work 15 years ago due to a career change. I was suddenly asked at work to produce these RS232 units within two weeks, at a Company that uses PGA's but not PIC's hence very little expertise and no programming equipment available for these devices. My spares box contains all the chips I need except for the UARTS which are no problem to get. It would take me more than two weeks to get into PIC programming let alone using a type with a UART which I am told will take longer to master. Then I have to buy all the paraphernalia to develop and program these devices so I considered it a none starter.For those who have mastered these devices then I take my hat off to you and humbly give my respect but I did not expect to be ridiculed just because the only thing firmly set in my ageing brain is BASIC and Z80 machine code. Maybe when I retire in two years time I may be able to sit in the kitchen and learn more about the versatile PIC but for now, I have to rely on what knowledge base I have. I did expect this Forum to maybe give me a little guidance from those more familiar with the 6402 rather than be ridiculed, I apologise for getting the reason for this Forum wrong and maybe I shall come back to it when I have mastered the PIC, if indeed that is a requirement for posting here.
May I close by saying that not all is bad from the past, the putting together of separate circuits can indeed be quite fun, it is a pity that others do not share this idea and resort to belligerency. My grateful thanks to those who have given more positive advice on the threads topic, it is appreciated.
Les

 

It would only take you a couple of days (if that) to 'get in to' PIC programming, they are very simple to use - and if you've had previous experience on Z80, you shouldn't find it very taxing. Using the hardware UART is trivial, as its doing it in software without a hardware UART. Your requirement is VERY, VERY simple, and my existing tutorials do almost everything you want to do, and if not exact, could be made to do so in only a few minutes.

The reason you've not received lots of help for your antique solution is that it's like asking for help building a 555 timer using valves back in the 80's - everyone thinks it's a bad idea.

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Topcat: A couple years ago, my team and I was tasked to design a simple serial optical communication system for a ship to air missile system. The receiver in the missile head was a simple slave much like the one you are proposing. We based our design on the RS232 protocal, using one start/one stop bits. Since the receiver was a simple slave, we succeded by using a minimalist approach, just a linear shift register and some very simple control. The task was made simpler by being synchronous. There was no microcontroller, no UART, no programming, no download to flash memeory, no code to maintain...My point here being that simple electronic solutions are still viable in the age of "everything must be done w/microcontrollers", or else at least with a high level of integration.

Highly integrated solutions certainly have their place, and of course, many innovations would not be possible without them. But I would argue that microcontrollers have made not electronic design and deployment obsolete. There remains many design situations that are most easily accomplished with electronic solutions. Look at it this way: for how long have we heard the death knell ringing for RS232? So-called "advanced" serial communication systems ( USB, 1394, i^2C, etc. ) was supposed to relagate RS232 to historical footnote. And yet, RS232 continues to thrive, even despite the fact that it's no longer installed on PC's. BTW, I had to go out and spend over 30 bucks for a USB-2-RS232 convertor for my projects. Why should I have to convert a supposed superior system to an inferior one???? Why indeed! This simple, "antique" protocal remains very viable despite all the calles for it's disposal. Indeed, integrated chips are still being developed for this portocal!

Sometimes, you simply must be deaf to the ridicule and sneers from those who have become a little too enamored with a single solution to everything. It's not true that everyone thought your solution was a bad one. I would continue to support your effort to get this up and running. I'm not sure I completely understood your requirements, but I would have continued to work with you to make sure I did.

I am reminded of a story I read recently in the "Tales From The Cube" segment of EDN magizine. A hardware engineer needed a simple kill switch for his system, and had two signals to use to kill the system ( one signal was a "key" switch and the other came from some other part of the system ) Anyway, he specified a simple "OR" gate for the circuit, to combine the two signals. His manager, a code-writer, thought his design was too primative, and didn't allow for expansion and flexibility. And so, by the time the manager got through 'fixing' the deisgn, the simple OR gate had grown into a multiplxer, along with the logic to generate the select vector and a bunch of 'unused' inputs. The original, simple circuit grew into an overly complex one full of unnessary 'features.'

The bottom line is that just because there is some sort of perceived 'advanced' solution, that doesn't mean it's always the best one. It only takes a little reasoning to know when your simple solution isn't appropriate, and a more integrated approach is needed.

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