Pic-c Variables

[yavuzselimaydin]

Hi guys;

I am working on a robot project and have a problem which is:

There are two microcontroller system and first one is scanning a 12*8 keypad, that pic gets the adress of key and sends data to other pic in i2c routines. Upto number 63 in decimal everything is ok, but above 63 the data is corrupted, if i explain in this way;

(64)decimal = (40)hex = (01000000)bnry, but the number above 64 becomes such: (64)decimal = (11000000)bnry in i2c data transfering.

I could not find mistake, thanks in advance....

[Banfa]

You have described the problem but not provided any context, I can not believe that the fact the corruption starts at the first value where bit 7 is 1 rather than 0 which suggests a problem in the way the i2c is being driven/configured.

Have you tried other numbers >64? are they corrupted in the same way (i.e. bit 8 set erroneously)? Have you tried the value 128 ( = 80 hex = 10000000 binary)?

[yavuzselimaydin]

Thanks for your interest, Banfa.

I tried your advice, for 128 there seem to be no mistake. I am beginner in c programming and wonder if that problem can cause because of choosing wrong variables, i thought "unsigned char" may be enough for variables in program for such a 8-bit microcontroller.

Good lucks in yoru jobs....

[Banfa]

unsigned char is probably fine, it is 8 bits in most systems although there are some systems in which it is 7 or 9 bits. However you should be able to verify the number of bits in your bytes easily by looking for the symbols

#define CHAR_BIT 8 /* number of bits in a char */
#define UCHAR_MAX 0xff /* maximum unsigned char value */

in limits.h in the headers supplied with your compiler.