fscanf vs fread for reading individual bytes from an RS232 object

Hi,

Recently I was trying to communicate with an instrument over RS232 to read some voltages from an ADC channel. With the following code

…

myData = fscanf(rs232DPCObject,'%c',6);

                  if (myData(2)*1 == DPC.ExtADA0ReadAddress)
                      if length(myData) == 6
                          integerData = (myData(3) + myData(4)*2^8 + myData(5)*2^16 + myData(6)*2^24);

                          docExtAD0Reading = [docExtAD0Reading typecast(uint32(integerData),'single')];
                  docExtAD0ReadingBinary = [docExtAD0ReadingBinary ; dec2bin(uint32(integerData),32)];

…

Most of the time, everything is fine and I read the voltage correctly. However, at some voltage levels some -significant- bits start to flip back and forth between 1 and 0, for example, at some fixed voltage level I read:

 docAD0ReadingBinary =

0011111101 0 110010111110110100110

0011111101 0 110010111110110100110

0011111101 0 110011001001100011001

0011111101 1 110010001100011010000

0011111101 1 110010001100011010000

0011111101 0 110011011101000100011

0011111101 0 110011011000000001111

0011111101 0 110010111110110100110

0011111101 0 110010111110110100110

0011111101 1 110010001100011010000

0011111101 0 110011011000000001111

0011111101 0 110011011101000100011

0011111101 1 110010001100011010000

When I replaced

myData = fscanf(rs232DPCObject,'%c',6);

with:

[myData, count, msg] = fread(rs232DPCObject, 6, 'uint8');

The problem was resolved… It seems that the problem is related with fscanf function. Could you please provide an explanation for the source of this problem? Might there be a bug in fscanf or do I use it inappropriately?

Best regards,

Evrim Onur ARI

[dpb]

I believe only knowing the details for the DUT transmission protocol would allow anybody to address the question. I suspect if it works reliably w/ fread but not w/ fscanf that it isn't actually ASCII and you're having trouble owing to that difference.