Hi Bill,

>Piclist,
>    Anyone know what windows 3.1 terminal program actually sends out the
>serial port?  I am trying to send data characters 0-9, but don't quite
>recognize what I see on the scope.  I've set up communications setting to
>7-n-1.
>Any input or pointers to info websites would be much appreciated.

This has been out for a few days and nobody's responded yet, so, I'll give
it a shot.

Data sent from the PC's RS-232 Serial Port is sent in the following format:

--------+    +----+----+      +----+----+----+------------    "1"
        |    |    |    |      |    |    |    |
        | SB | D0 | D1 |  ... | Dn | PB | TB |
        |    |    |    |      |    |    |    |
        +----+----+----+      +----+----+----+                "0"

Where:

"SB"        - Start Bit (Always Present)
"D0"..."Dn" - Data Bits (Typically 8)
"PB"        - (Optional) Parity Bit
"TB"        - Stop Bit (1 or 2)

But, at RS-232 levels, a "1" is at -12V and a "0" is at +12V
(approximately).  So "A", being sent via RS-232, on an oscilloscope will
look like:

         +----+    +----+----+----+----+----+    +----+             +12V
         |    |    |                        |    |    |
         |    |    |                        |    |    |
         |    |    |                        |    |    |
---------+    +----+                        +----+    +----+------- -12V

          SB=0 D0=1 D1=0 D2=0 D3=0 D4=0 D5=0 D6=1 D7=0 TB=1

I suspect this is what you are seeing and you can't make heads or tails of
it (hopefully this will give you a better idea).

OR...

You have "Hardware Handshaking" enabled on your PC and nothing is coming out
of the serial port except for the -12V on the Transmit line.  Disable
Hardware Handshaking in the Terminal Program or tie together DSR/DTR and
CTS/RTS at the PC's Serial Port Connector.  The problem in this case is the
PC's BIOS is expecting the handshaking lines at a specific state before data
can be sent.  By tying these bits together (or getting rid of the check) it
will be able to transmit without any problems.

For the PIC side, you will have to level shift the +/- 12V logic to 5/0V
CMOS logic using something like a Max2x2.

Good luck,

myke

"If people don't know what you're doing, they don't know what you're doing
wrong." - Sir Humphrey Appleby K.C.B