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piripic
Joined: 15 Jan 2008
Posts: 25
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| help, how to cast signed variable ? |
 Posted: Tue Jul 01, 2008 2:58 am |
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Hi, I am in trouble to understanding how to make to work this example. Can anyone explain to me how to cast (if possible) signed variables ? Thanks
Claudio
| Code: | #include <16F877.H>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 8000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
//------------------------------------------------------------------------------
// Return the temperature in ° centigrade
signed int8 TempRead(int8 valore)
{
// Temp [°C] = -40 + (68.4 - TEMP READBACK) × 9.32
signed int32 temperat, temper32;
int16 temp_rd;
// To avoid floating point numbers I multiply all values by 100
temp_rd = ((int8)valore & 0x7F);
temper32 = 6840 - temp_rd * 100;
temperat = -4000 + temper32 * 932;
temperat /= 100;
#asm
BSF &(int8)temperat,7 // Set bit 7 of temperat LSByte
BTFSS &(int8)temperat+3,7 // Skip if MSB (bit 31 of temperat) = 1
BCF &(int8)temperat,7 // Clear bit 7 of temperat LSByte
#endasm
return (signed int8)temperat;
}
//======================================
void main()
{
signed int8 mytemp;
int8 value;
while(1) {
while(!kbhit()) ;
value = getc();
mytemp = TempRead(value);
printf("Value = %u \n\rTemperature = %d \n\r", value, mytemp);
}
} |
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Ttelmah
Guest
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| Posted: Tue Jul 01, 2008 5:16 am |
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I don't think you mean 'cast', possibly just 'output'?.
'casting', is forcing the conversion of a variable into another type. So (for example), you can take a sum like:
| Code: |
int8 a,b;
int16 val;
a=100;
b=100;
val = (int16)a*b;
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Which forces 'a' to be converted into an int16 type, before the arithmetic is performed (and thereby forces 'int16' arithmetic).
I suspect what you are asking is how to output a 'long' type?. The answer is 'L'.
So:
| Code: |
printf("%Ld/n/r",val);
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Switches the output to support the 'long'.
'd', and 'x', _default_ to assuming the value is 'signed'. If you want to use unsigned values, you use 'u' (which you are already doing).
Best Wishes |
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piripic
Joined: 15 Jan 2008
Posts: 25
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| Posted: Tue Jul 01, 2008 8:40 am |
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Ttelmah, thanks. I think I have found the mistake that I did.
For "cast" I meant to say... to pass a signed int32 to a signed int8. I believe that using the three assembly instructions all work good... I 'shift' the sign bit.
The example below seems to work... obviously the range of 'temperat' does not exceed the -128 +127...
| Code: | #include <16F877.H>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 8000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
//------------------------------------------------------------------------------
// Return the temperature in ° centigrade
signed int8 TempRead(int8 valore)
{
// Temp [°C] = -40 + (68.4 - TEMP READBACK) × 9.32
signed int32 temperat, temper32;
int16 temp_rd;
// To avoid floating point numbers I multiply values by 100
temp_rd = ((int8)valore & 0x7F);
temper32 = 6840 - (signed int16)temp_rd * 100;
temperat = (temper32 * 932) / 10000;
temperat += -40;
#asm // Now I 'shift' the sign bit
BSF &(int8)temperat,7 // Set bit 7 of temperat (least significant byte)
BTFSS &(int8)temperat+3,7 // Skip if MSB (bit 31 of temperat) = 1
BCF &(int8)temperat,7 // Clear bit 7 of temperat (least significant byte)
#endasm
return (signed int8)temperat;
}
//======================================
void main()
{
signed int8 mytemp;
int8 value;
while(1) {
while(!kbhit()) ;
value = getc();
mytemp = TempRead(value);
printf("Value = %u \n\rTemperature = %d \n\r", value, mytemp);
}
} |
Thanks again,
Claudio |
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