I could be out of date with this but RS-232 specs I have used in the past go 
from a + level to a -level. 0 volts is an invalid condition.
I would put a scope there to see.

John Ferrell    W8CCW
"My Competition is not my enemy"
http://DixieNC.US

----- Original Message ----- 
From: "Przemyslaw Lopaciuk" <pic@amusementcity.com>
To: <piclist@mit.edu>
Sent: Friday, January 12, 2007 3:43 PM
Subject: [EE] Very odd problem with RS232...


> Hi,
> I've encountered very odd thing with RS232 and I'm stuck... I don't have 
> any idea what can be the problem..
> I want to read information from RS232 ... I use 9600 baud rate, hardware 
> and software handshaking.
> The sequence looks like that...
>
> 1) DTR and RTS high. PC sends 0x80, Device sends 0x01 back
> 2) PC sends 0x81, Device sends 0x00 back.
> 3) PC sends 0x01 and then lowers DTR
> 4) PC sends 0x12, device sends 8 bytes back ( some information )
>
> It works perfectly on PC but when I use my board it doesn't. When using 
> the board I can get through step 1 and step 2. I can't get the 8 bytes 
> from thep 4 though. When I test the board connecting it to PC the data 
> goes through correctly.
>
> I even thought that it might be voltage ( I've got 7,5 V on my board ), so 
> I put resistor on the cable and lowered the voltage to 7,5 V from PC ( it 
> is 12 normally ). The PC can still get data from the Device.
>
> I don't know where did I make the mistake. Maybe I don't know something 
> about RS232 standard?
>
> Please help.
>
> Thank you in advance.
>
> Sam
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