Communication between PIC 16f877a and MATLAB

[PCM programmer]

Look at the crystal. Post the markings that you see on the crystal.
Also post the markings on the capacitors for the crystal.

Or post a link to a sharp, infocus, hires photo of the crystal and capacitors.
Use an image hosting website such as imgur.com to hold the image.

[temtronic]

I'd change the Realterm baud rate, say to 4800, 19200, etc. and see if you get the correct '123' data.

let's say at 4800, you do get 123...
then you know the speed of the clock is off exactly by a factor of 2, so you may have an 8MHz xtal. The other common xtal was 20 MHz.

Hopefully you can SEE the number on the xtal though, something like 4.00, 8.00, 20.0. My like would be the xtal is soldered to the PCB with the marking towards the PCB......

[Ttelmah]

Are you sure Y1, is actually a crystal?. Reason I ask, is HS turns up the
drive to the oscillator. Now, ceramic resonators often need a higher
drive than genuine crystals.
I really would look at the crystal with a magnifier, and see what it says.

It wouldn't be beyond belief that somebody has substituted a faster
crystal than the circuit shows. This then needs the higher drive, and
gives the wrong baud rate.

Do the most basic test. The 'flash an LED' program. Simple code to
turn a pin on for one second, then off for one second. Test with a scope
or by putting an LED (with a suitable resistor) on the pin. Time how long
ten flashes take.

I suspect you are not actually running at 4MHz.

Other possibility is your connection is wrong.
How are you connecting to the PC?.
Presumably something like a USB to serial adapter?.
If so is this USB-RS232 or USB-TTL.
If it is USB-RS232, you need an RS232 adapter between the PIC
and the module.

You may simply have inverted data.

[S1gnature]

To PCM Programmer, Ttelmah, temtronic : The problem is I didn't check the REAL crystal carefully. Thank all of you for those suggestions!
I just borrowed a magnifier and check on the crystal, it said 8 0 0. So I change the frequency to 8M in CCS. This is a quite valuable experience to me.
Everything now works like a charm.
I also make change to the program, now the PIC sends data everytime I push a button instead of constantly sending data. The result is now good.



Thanks temtronic for your suggestion about RealTerm. It saves a lot of time.

Also in MATLAB, now it receives the strings sending from the PIC. I would like to ask one more question:


In MATLAB, I successfully receive the strings, but it is in form

[Ttelmah]

It had all the symptoms of 'wrong frequency'...

Glad you have found it. Lesson is 'check everything'....

On the numbers, I suspect somewhere in the MPLAB settings, you are telling
it to only use 3 digits, so it is just taking 3 digits, and then accepting this
without needing the terminator.

[temtronic]

Hay, it's GREAT to see you got it working !!! 8.00 MHz is another 'popular' xtal for PICs.
I used to put a small drop of nail polish on the top of xtals to colour code them. yellow = 4 MHz.

[S1gnature]

Thank you temtronic and Ttelmah . I feel great when everything works too, even it's just my curiosity about how this thing works. I borrow the development board from my nephew as he left it in the store room. This is the first time I work on both software and hardware. Now I'm trying sending data from PC to PIC to control some devices. It is quite interesting.

[PCM programmer]