At 13:54 14/07/97 +1300, you wrote:
>Greetings All !!
>
>I am new to PICs and electronics.
>
> I have managed (after many attempts with the help of you people )  to
>programme a PIC to  read a voltage  from a port through AD converter
>(PIC16C71) use calibration constants to give pressure in mbars and store
>those  readings in the data memory.
>
>Could someone please explain to me in LAYPERSON terms how can I
>extract these data using a Personal Computer.
>
>I have read many serial comm. notes sent through  the PIC list and
>application notes ,  but have a problem of understanding them.

OK, here goes..

First the hardware. The RS-232 port uses two voltages levels to transmit
data, one represents 0 and the other 1. Usually these are around +/- 12
volts. Fortunately there is a chip available (the MAX232) which includes a
charge pump and all the bits to convert from 5 volts to +/- 10 volts. It's
helpful to get the data sheet for this, unfortunately you're a bit too far
away to just pop one in the post.

Once you have got the hardware to convert from RS-232 to TTL voltages the
next bit is to send some data.

Typically I use 9600,n,8,1. That is 9600 bits per second, no parity, 8 data
bits, one stop bit.

9600 bits per second means each bit is 104.17 micro seconds wide and you
will have to time these bits with the PIC (unless you use a 16C73 which has
a built in USART)

Each byte commences with a start bit (104 microseconds wide), then eight
data bits (same width) than a stop bit (another 104 microseconds). Your PIC
has to send it's data this way, and it is picked up by the PC. I just use
the old fashioned Windows terminal to see what I'm sending.

You can either send your data in binary format, or convert it to characters
and send them. Either way you should add a checksum to test for data
corruption. I would suggest starting by converting to characters because
it's easy to work out what's going wrong.

Hope this is some help, If it's not clear mail me and I'll try sending you a
sketch.

Keith.



==========================================================
Keith Dowsett         "Variables won't; constants aren't."

E-mail: kdowsett@rpms.ac.uk
   WWW: http://kd.rpms.ac.uk/index.htm