Laptop Serial Coms Crisis.......

May 31, 2004 3 Replies
R

Well I say crisis,



Hi all.



I just wanted to know if anybody has had a problem with Laptop serial ports.



I currentley have a pic16f873 with hardware uart and pwm driving 2 motors on my bot base. My desktop machine communicates with the pic through a max232 fine but the laptop gets a single character ok but also receives ascii 256 I think.



If a string of chars is sent from the pic the laptop get junk chars. The pic receives chars from the laptop ok though.



I also get framing errors.



Im writing my own comms s/w with VB6 and MSComm.ocx



Using the compiled exe on both machines but different results.



HELP



Cheers Rob


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R

The problem is almost certainly with your VB app, not the serial ports as such. You'll need to improve the handling on the PC side (circular buffer, perhaps) or maybe just use a lower baud.

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R

Cheers for the tips Rich.

I don't know anything about programming comms. This is my first go. My pic goes pants up if you sent it info to quick. What I don't understand is why it works on the desktop but not the laptop.

I'll try a low baud rate to start with and find some info on VB comms programming.

Thanks again for the tips. Rob of robsbots

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R

-------------------- Listen: Laptops are terrible for that, they use LOW voltages for the serial port drive voltage and it falls out under any load at all. They use +5 to +7-9 V for the +12V, and they use -5V for the -12V, and their weak DC-DC converters can't push it. Just add buffers to the existing outputs, or use pullups on them if they screw up, and you will have less problems, and keep the current load tiny, logic only.

-Steve

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