Serial Out from PIC to PC without a driver?

AlexR

Joined Jan 16, 2008
732
The PIC can't supply RS232 levels without a driver, however the PC is a Microsoft designed device and so does not conforming to any established standards. It will therefore accept logic level signals on its com port.
The main reason for using an RS232 driver with a PIC USART when talking to a PC is to invert the signal. The RS232 standard specifies a mark condition as -12Volt and a space as +12Volt, the USART outputs a logic 1 (5Volt) for a mark and logic 0 (0Volt) for a space.
The project gets around the inversion problem by not using the PIC USART and writing its own comms program with the level inversion built into the software.
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,830
Wow that seems an awful lot of trouble to save buying a chip! :)


I had a similar problem years ago. I had an Atari 800 and BBS had just come on to the scene plus I was going to college and I has able to do this most amazing thing of dialing up and connecting to our mainframe to do my homework.

Someone had given me an old acoustic coupled modem but Atari had a modified SCSI out and no RS232. You could purchase an RS232 interface for $100 or so but I did not have $100 or so. I went to Rat Shack (back in the day when they carried most things) and purchased a couple of Rs232 line drivers and receivers. I then wrote my own device handler in assembler and was up connected to want was to become the world wide web in no time.

Atari made building the device driver easy. That was a great OS. Can't remember how I got around device IDs, My interface was dumb and most others had some intelligence to them by announcing their device ID. I may have been able to write that into the driver. Can't rememebr for sure.
 

t06afre

Joined May 11, 2009
5,934
How stable/deterministic is such a system? I for sure would never have designed a RS232 system without proper RS232 signals levels.
 

n9352527

Joined Oct 14, 2005
1,198
It might work, it might not. I had a desktop that won't talk to such circuit. And two old laptops that would. Not something that I will put in commercial products.
 
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