Dear all,

I have simple modbus example below.I am using arduino Uno & RS485 sheild for programming. The code compile & execute successfully. I am facing problem while reading -ve value. it read eqivalent unsigned value. How can save /read signed variable here.


This what i read
65533 for -3
65532 for -4
655535 for -1.

IS any conversion i can to read negative equivalent value. what changes i need to make.

1. #include <ModbusRtu.h>
2. 
   
3. // data array for modbus network sharing
4. uint16_t au16data[16] = {
5. 3, -3, -4, 4, 2, 7182, 28182, 8, 0, 0, 0, 0, 0, 0, 1, -1 };
6. 
   
7. 
   
8. Modbus slave(1,0,0); // this is slave @1 and RS-232 or USB-FTDI
9. 
   
10. void setup() {
11. slave.begin( 9600 ); // baud-rate at 19200
12. }
13. 
    
14. void loop() {
15. slave.poll( au16data, 16 );
16. }

 

The bits are same regardless of their treatment as signed or unsigned. If you assign all 1's to an int it will be interpreted as -1. If you assign it to an unsigned it will be interpreted as 65535.

 

Change line 4 to int16_t