BUilding a signed 32 bit number

[ringo42]

I'm sending a signed 32 bit number froma pc Via serial port as 4 bytes.
I can send a number from -32767 to 32767 and everything is fine, however if I send a 32768 the pic interprets it as a 0, a 32769 it thinks is a -1, etc

The PC side appears to be working,
if I send a 1 it sends 1 0 0 0.
If I send a 256 it sends a 0 1 0 0
If I send a 32768 it send a 0 80 0 0
if I send a -1 it send a FF FF FF FF
if I send a -2 it send FE FF FF FF

On the pic side I have tried:
R_goal_position=Rposition+make32(command_byte_5,command_byte_4,command_byte_3,command_byte_2);

and this
temp_pos_long=0;
temp_pos_long=temp_pos_long|command_byte_5;
temp_pos_long=(temp_pos_long<<8)|command_byte_4;
temp_pos_long=(temp_pos_long<<8)|command_byte_3;
temp_pos_long=(temp_pos_long<<8)|command_byte_2;
R_goal_position=Rposition+temp_pos_long;

Any ideas here why apparantly a 15bit number is ok, but beyond that it gets wacko??
Thanks
RIngo
___________________________
This message was ported from CCS's old forum
Original Post ID: 13636

[PCM programmer]

:=I'm sending a signed 32 bit number froma pc Via serial port as 4 bytes.
:=I can send a number from -32767 to 32767 and everything is fine, however if I send a 32768 the pic interprets it as a 0, a 32769 it thinks is a -1, etc
:=
-----------------------------------------------------------

You may not know that a "long" in CCS is an unsigned 16-bit
number. Also, all CCS data types default to "unsigned".
This is different from MSVC, etc.

To do a signed 32-bit number, you have to declare it like this:

signed int32 temp;


The following test program works fine. It displays "-2".

<PRE>
#include "c:\Program Files\Picc\Devices\16F877.h"
#fuses HS, NOWDT, NOPROTECT, PUT, BROWNOUT, NOLVP
#use Delay(clock=8000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
<BR>
//====================================================
void main()
{
char byte_2;
char byte_3;
char byte_4;
char byte_5;
signed int32 goal;
<BR>
byte_2 = 0xFe; // LSB
byte_3 = 0xFF;
byte_4 = 0xFF;
byte_5 = 0xFF; // MSB
<BR>
goal = make32(byte_5, byte_4, byte_3, byte_2);
<BR>
printf("Hex result = \%lx\n\r", goal);
printf("Decimal result = \%ld\n\r", goal);
<BR>
while(1);
}
</PRE>
___________________________
This message was ported from CCS's old forum
Original Post ID: 13639

[R.J.Hamlett]

:=:=I'm sending a signed 32 bit number froma pc Via serial port as 4 bytes.
:=:=I can send a number from -32767 to 32767 and everything is fine, however if I send a 32768 the pic interprets it as a 0, a 32769 it thinks is a -1, etc
:=:=
:=-----------------------------------------------------------
:=
:=You may not know that a "long" in CCS is an unsigned 16-bit
:=number. Also, all CCS data types default to "unsigned".
:=This is different from MSVC, etc.
:=
:=To do a signed 32-bit number, you have to declare it like this:
:=
:=signed int32 temp;
:=
:=
:=The following test program works fine. It displays "-2".
:=
:=<PRE>
:=#include "c:\Program Files\Picc\Devices\16F877.h"
:=#fuses HS, NOWDT, NOPROTECT, PUT, BROWNOUT, NOLVP
:=#use Delay(clock=8000000)
:=#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
:=<BR>
:=//====================================================
:=void main()
:={
:=char byte_2;
:=char byte_3;
:=char byte_4;
:=char byte_5;
:=signed int32 goal;
:=<BR>
:=byte_2 = 0xFe; // LSB
:=byte_3 = 0xFF;
:=byte_4 = 0xFF;
:=byte_5 = 0xFF; // MSB
:=<BR>
:=goal = make32(byte_5, byte_4, byte_3, byte_2);
:=<BR>
:=printf("Hex result = \%lx\n\r", goal);
:=printf("Decimal result = \%ld\n\r", goal);
:=<BR>
:=while(1);
:=}
:=</PRE>
And of course, you can tidy up the access a lot, by using a union.
So:
union {
int8 b[4];
signed int32 word;
} goal;

Then you can use:
goal.b[0] to access the first byte of the value,
goal.b[n] to access any byte you want, and
goal.word to access the entire 32bit variable.

Makes things a lot 'tidier'. :-)

Best Wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 13650