I've got a peculiar situation here that I'm figting with that I hope someone can help me with. I'm using the Silicon Labs IDE, SDCC, and the Silicon Labs 8051F340. When I refer to "checking values" below I am using printf to send the data out over the serial port to another PC listening with Hyperterm.

I've got a structure defined like this:

(main.h)
struct ContactType {char id; int bearing;};
extern xdata struct ContactType Contact[10];

(main.c)
xdata struct ContactType Contact[10];


I go on to populate Contact inside my external interrupt handler (the data comes in over the UART and is signalled ready via the external interrupt). The code is similar to this:

...
Contact[0].id = '5';
Contact[0].bearing = 360;
...
draw(CONTACT_SCREEN); // send the data to the LCD

I have checked the data right before the call to draw() and it is as expected, 5, 360. Then I check right away inside draw() and my data is 5, 360. Then a bit later inside draw() when I get around to using the data, it is 5, 256.

Any ideas on how and why this value is changing?