problem with shift_left.....

[John Morley]

Hi all,

Compiler version: 3.162

I am using shift_left to clock 8 bits of data out of a peripheral device, MSB first. The problem is that when I get the 8th bit, the variable that the data is going into rolls over to a negative number. I seem to be doing it exactly the way numerous examples in the manual do it, but mine has this undesired behaviour. BTW, the data variable is define as:

int data;

I show the routine I am having a problem with first, and then the output of a printf to show what's going on. As you can see from the output, all seems to be well until the 8th bit....


for(ctr = 1 ; ctr <= 8 ; ++ctr)
{
output_high(SCLK); // Clock to high
delay_us(20);
shift_left(&data,1,input(SDATA));
output_low(SCLK); // Clock to low
printf("ctr, bit, data: : \%i \%i \%i\n\r", ctr,input(SDATA), data);
}
output_low(SDATA); // Acknowledge the 1st byte to be driven by the SHT1x
output_high(SCLK);
delay_us(20);
output_low(SCLK);


Output:

ctr, bit, data: : 1 1 1
ctr, bit, data: : 2 1 3
ctr, bit, data: : 3 1 7
ctr, bit, data: : 4 0 14
ctr, bit, data: : 5 0 28
ctr, bit, data: : 6 0 56
ctr, bit, data: : 7 0 112
ctr, bit, data: : 8 1 -32

Thanks for looking!

John
___________________________
This message was ported from CCS's old forum
Original Post ID: 144515473

[Neutone]

:=Hi all,
:=
:=Compiler version: 3.162
:=
:=I am using shift_left to clock 8 bits of data out of a peripheral device, MSB first. The problem is that when I get the 8th bit, the variable that the data is going into rolls over to a negative number. I seem to be doing it exactly the way numerous examples in the manual do it, but mine has this undesired behaviour. BTW, the data variable is define as:
:=
:=int data;
:=
:=I show the routine I am having a problem with first, and then the output of a printf to show what's going on. As you can see from the output, all seems to be well until the 8th bit....
:=
:=
:= for(ctr = 1 ; ctr <= 8 ; ++ctr)
:= {
:= output_high(SCLK); // Clock to high
:= delay_us(20);
:= shift_left(&data,1,input(SDATA));
:= output_low(SCLK); // Clock to low
:= printf("ctr, bit, data: : \%i \%i \%i\n\r", ctr,input(SDATA), data);
:= }
:= output_low(SDATA); // Acknowledge the 1st byte to be driven by the SHT1x
:= output_high(SCLK);
:= delay_us(20);
:= output_low(SCLK);
:=
:=
:=Output:
:=
:=ctr, bit, data: : 1 1 1
:=ctr, bit, data: : 2 1 3
:=ctr, bit, data: : 3 1 7
:=ctr, bit, data: : 4 0 14
:=ctr, bit, data: : 5 0 28
:=ctr, bit, data: : 6 0 56
:=ctr, bit, data: : 7 0 112
:=ctr, bit, data: : 8 1 -32
:=
:=Thanks for looking!
:=
:=John

So the printf function is showing a signed interger instead of an unsigned interger? Verify the printf function call is formatted correctly. If you were shifting in a signed byte it worked fine.
___________________________
This message was ported from CCS's old forum
Original Post ID: 144515475

[Sherpa Doug]

It looks like a printf problem. Try printing the result in hex instead of decimal to see what the actual bits are.

:=Hi all,
:=
:=Compiler version: 3.162
:=
:=I am using shift_left to clock 8 bits of data out of a peripheral device, MSB first. The problem is that when I get the 8th bit, the variable that the data is going into rolls over to a negative number. I seem to be doing it exactly the way numerous examples in the manual do it, but mine has this undesired behaviour. BTW, the data variable is define as:
:=
:=int data;
:=
:=I show the routine I am having a problem with first, and then the output of a printf to show what's going on. As you can see from the output, all seems to be well until the 8th bit....
:=
:=
:= for(ctr = 1 ; ctr <= 8 ; ++ctr)
:= {
:= output_high(SCLK); // Clock to high
:= delay_us(20);
:= shift_left(&data,1,input(SDATA));
:= output_low(SCLK); // Clock to low
:= printf("ctr, bit, data: : \%i \%i \%i\n\r", ctr,input(SDATA), data);
:= }
:= output_low(SDATA); // Acknowledge the 1st byte to be driven by the SHT1x
:= output_high(SCLK);
:= delay_us(20);
:= output_low(SCLK);
:=
:=
:=Output:
:=
:=ctr, bit, data: : 1 1 1
:=ctr, bit, data: : 2 1 3
:=ctr, bit, data: : 3 1 7
:=ctr, bit, data: : 4 0 14
:=ctr, bit, data: : 5 0 28
:=ctr, bit, data: : 6 0 56
:=ctr, bit, data: : 7 0 112
:=ctr, bit, data: : 8 1 -32
:=
:=Thanks for looking!
:=
:=John
___________________________
This message was ported from CCS's old forum
Original Post ID: 144515478