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Harry Mueller
Joined: 17 Oct 2005
Posts: 116
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| declaration, combining bytes or formating error? |
 Posted: Thu Mar 16, 2006 5:49 pm |
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I'm reading the data output from an SRF08 in 2 bytes, the high byte first and the low byte second. I'm combining the two bytes and saving the value in an int16 array[17]. When I print the values using "%lu" to format the output I only get the low byte or only printing one byte, I'm not sure which.
Here is my code: | Code: | #include <16F877A.H>
#fuses HS, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 20000000)
#use i2c(Master,sda=PIN_C4,scl=PIN_C3)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
main()
{
int i;
int16 range[17];
while(1)
{
i2c_start(); //initate start condition
i2c_write(0xE0); //device address
i2c_write(0x00); //register address
i2c_write(0x50); //set units to inches
i2c_stop();
delay_ms(105); //wait for returning ping
i2c_start(); //initiate a new start condition
i2c_write(0xE0); //device address
i2c_write(0x02); //address of high byte register
i2c_start();
i2c_write(0xE1); //device address but read
for (i=0;i<17;i++)
{
range[i] =i2c_read(1) << 8; //read first byte and shift left
if(i<16)
range[i] += i2c_read(1); //read second byte and add to 1st
else
range[i] += i2c_read(0);
}
i2c_stop();
for (i=0;i<17;i++)
printf("range in inches = %lu\n\r", range[i]);
delay_ms(1000);
}
}
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Thanks, Harry |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Mar 17, 2006 1:36 am |
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You should be able to fix it by casting the i2c_read(1) result to a 16-bit
value before doing the left shift. I think the problem is that CCS
can't be depended upon to do automatic type promotions, as is done
by MSVC, etc. Sometimes CCS does them and sometimes they don't.
| Quote: |
range[i] =(int16)i2c_read(1) << 8;
if(i<16)
range[i] += i2c_read(1);
else
range[i] += i2c_read(0);
}
i2c_stop();
for (i=0;i<17;i++)
printf("range in inches = %lu\n\r", range[i]);
delay_ms(1000);
} |
If you want to be really safe, you could cast the other two i2c_read()
lines to (int16) as well.
-------------------------------------
In the other thread with the translated driver code, I initially had
a cast to int16 in there, but I decided check the .LST file and see if
it worked without it, and it did, so I took it out of the code that I posted.
But what if your compiler version needs it ? If you want to be really
safe you could change the SRF08 driver code to this:
| Code: | range[i] = ((int16)i2c_read()) << 8;
range[i] += (int16)i2c_read(0); |
See if it improves your results. |
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rnielsen
Joined: 23 Sep 2003
Posts: 852
Location: Utah
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| Posted: Fri Mar 17, 2006 10:08 am |
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| Quote: | range[i] =i2c_read(1) << 8; //read first byte and shift left
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This line will read data from the i2c bus and then shift it eight places which will then be all 0's. This is _then_ stored in range[].
Try reading the data, storing it into range[] and then shifting range[]. Now read the second byte from the i2c bus and store that into the lower half of range[].
Ronald |
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Harry Mueller
Joined: 17 Oct 2005
Posts: 116
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| Posted: Fri Mar 17, 2006 1:08 pm |
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Thanks PCM and Ronald,
I've tried both solutions and they both work!
Regards, Harry |
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