Xbee Wireless Interface Tutorial




Questions & Comments?

very helpful thanks

Hello,

I built the Xbee interface using PIC18F4550 instead of using PIC18F4250. When I try and load the Hex file on to the pics I get an error saying:

Writing program memory successful
mismatch in 32-byte chunk at 0x00000000:
File: ################5cef08f01200####################################
Device:2cef04f01200120004ef08f012000000ffffffffffffffff0cef08f012000100
Program memory contains errors!

I am using FSUSB to program the PIC, this is the RX code. I changed the #include <p18f4250.h> to #include <p18f4550.h>.

Any ideas?

Hi,

This sounds like there's a problem with your programmer.

Does a simple program like an LED flasher work?



If something like the program seen above, compiles and programs successfully onto the 4550, then either something in MPLAB is set incorrectly, or my software for the XBEE modules needs to be modified to be compatible with that version of the PIC.

The code you just give me complies and programs perfectly. I didnt think there was much of difference in using the 4550.

The transmitter code compiles and seems to load up fine. Its the Receiver code, it compiles fine but when I program it using FSUSB through the linux terminal it gives me the above error.

There really isn't, I just can't imagine why MPLAB would spit that out. It's a problem I've never run into.



My only guess is that it's a programmer problem. Maybe try programming on a windoze box?

Another option would be to re-write the code piece by piece, compiling and downloading to the PIC until you get that similar error again. Then you'll know what part of the code might be causing the problem, since other programs seem to download fine.

::EDIT::

Apparently the FSUSB programmer relies on a bootloader to program the PIC which will have re-mapped your interrupt vectors. My bet is if you deleted all of the interrupt related code for the receiver, compiled and downloaded it to the PIC it would work just fine.

You'll have to lookup the new address for the High and Low Interrupt so that you can point it to the InterruptHandlerHigh() function.

Ok, so deleted the handler sections. and I still compiled and programmed. I am sure you are right about the Bootloader. I am lost on a work around for this.

I took a look at the User Guide for the FSUSB located here:
http://ww1.microchip.com/downloads/en/devicedoc/51526a.pdf
and I found the following:


My guess is that if you change the following section of the receiver code
FROM:

TO:


It should compile and download without any problem.

That did it. Thank you, your awesome.

I have another question for you, if you dont mind. Do I need to Configure my Xbee pros via the parallax usb adapter before this will work?

Xbee modules come set with default values, double check the data sheet if you're unsure. The default value for serial communication TX/RX is 9600 baud. So if you send 9600 BPS baud rate serial data to the transmitter Xbee's DIN pin you'll see the exact same thing come out of the receiver Xbee's DOUT pin.

Is there a way to do this without using interrupts?

Yes, but it wouldn't be very reliable because you would have to poll to check and see if the USART receiver buffer is ready/full. Depending on the timing you could potentially miss transmitted data.

However, if you still wanted to do it without interrupts then you would do everything in the main loop and included a forever while loop similar to this:

This is what I have so far:

Transmitter:
while(BusyUSART())
{
WriteUSART("Test");
DelClks(48000000 * 0.5);
}

Receiver:
unsigned char data;

while(!DataRdyUSART);
{
data = ReadUSART();
DelClks(48000000 * 0.5);
LcdDspChar(data);
}

I have gotten something like this to work but when it is displayed on the lcd it is scrambled.