Hello all,
Could anyone give me an example of how to convert a 32-bit integer into two 16bits? I am trying to send a negative value through Modbus TCP input register. My code works great just the input register won't show a negative value, instead shows some really big value when the Arduino updates a negative value.
I know this is not an Arduino issue, but was hoping someone could help me with this. This is the library I used.
Thank you
Gijo
My code works great
What code?
#include <ModbusIP.h>
#include <Modbus.h>
#include <Ethernet.h>
#include <SPI.h>
int PULC = 7; //define Pulse pin
int DIRC = 6; //define Direction pin
int ENAC = 5; //define Enable pin
float nC = 0;
float pC = 0; // variable for pot in center
int PULP = 2; //define Pulse pin
int DIRP = 3; //define Direction pin
int ENAP = 4; //define Enable pin
float nP = 0;
float pP = 0; // variable for pot in power
int power;
int power_zero;
int center;
int center_zero;
int potC = A0; // set analog pin A0 for pot for center
int valC = 0; // variable to read from pot
int potP = A1; // same for power
int valP = 0;
const int power_hr = 100; // makeing a holding register at 30101 for power value
const int center_hr = 105; // making a holding register at 30106 for center values
const int valC_ir = 110; // making a input register for pot pin center
const int valP_ir = 115; // making a input register for pot pin power
ModbusIP mb; // Modbus IP object
void setup()
{
Serial.begin(9600);
pinMode (PULC, OUTPUT); // set all pins as output pins
pinMode (DIRC, OUTPUT);
pinMode (ENAC, OUTPUT);
pinMode (PULP, OUTPUT);
pinMode (DIRP, OUTPUT);
pinMode (ENAP, OUTPUT);
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
byte ip[] = {192, 168, 1, 120};
mb.config(mac, ip); // config MODBUS IP
mb.addHreg(power_hr); // adding the holding register for power
mb.addHreg(center_hr); // same for center
mb.addIreg(valC_ir); // input register for center
mb.addIreg(valP_ir); // input register for power
power_zero = 5; // Hard coding the zero power value
power = 5;
center_zero = 0; // Hard coding the zero center value
center = 0;
potC = 0;
mb.Hreg(power_hr, power);
mb.Hreg(center_hr, center);
mb.Ireg(valC_ir, potC);
mb.Ireg(valP_ir, valP);
}
void loop()
{
mb.task();
power = mb.Hreg(power_hr);
center = mb.Hreg(center_hr);
if (power != power_zero)
{
moveinpower();
}
if (center != center_zero)
{
moveincenter();
}
delay(1000);
valC = analogRead(potC); // read the center pot pin
valP = analogRead(potP); // read the power pot pin
pC = map(valC, 0, 1023, -75,75);
pP = map(valP, 0, 1023, -75, 75);
mb.Ireg(valC_ir, pC);
mb.Ireg(valP_ir, pP);
/*Serial.print("Center Pot value: ");
Serial.println(pC); // for debugging
Serial.print("Power Pot value: ");
Serial.println(pP); // for debugging */
}
void moveincenter()
{
}
void moveinpower()
{
}
I am trying to get a negative value to output in the input registry.
The Arduino sends the correct value but since a negative value uses 32bits, can I maybe send two 16bit values into Modbus and maybe it can output a negative value?
There are two generally accepted ways of splitting integers.
uint32_t big_number = something;
uint16_t low_order_byte = big_number & 0xFFFF;
uint16_t high_order_byte = big_number >> 16;
union
{
uint32_t big_number;
struct
{
uint16_t low_order_byte;
uint16_t high_order_byte;
};
} new_name;
Assign new_name.big_number = something;
Then new_name.low_order_byte is the low order byte and new_name.high_order_byte is the high order byte.
The main difference being is that the shift operation has to be done explicitly while the union can be used repeatedly.