// This should be a basic slave, which will store pressure value from pin A0 for transmitting
// as well as receiving a value for setting a servo (Pin 6) open or close.

#include <SimpleModbusSlave.h>
#include <Servo.h>
Servo tankservo;
 
const int tankservoPin = 6;
int open = 180;
int close = 90;

int servo1State = 0;        // current state of the button
int lastservo1State = 0;    // previous state of the button

#define  LED 9 

enum 
{     
  TANK_PRES,
  CHAMB_PRES,
  SERVO1,
  SERVO2,
  SERVO3,
  SERVO4,            
  HOLDING_REGS_SIZE 
};

unsigned int holdingRegs[HOLDING_REGS_SIZE];

void setup()
{
  modbus_configure(9600, SERIAL_8N2, 1, 2, HOLDING_REGS_SIZE, holdingRegs);    
  tankservo.attach(tankservoPin);
}

void loop()
{
  modbus_update();
  holdingRegs[TANK_PRES] = analogRead(A0); 

 // digitalWrite(servo1State, holdingRegs[SERVO1]); unsure which to use - this is the original

servo1State = digitalRead(holdingRegs[SERVO1]); // unsure which to use - this is interpreted

if (servo1State != lastservo1State) {
    // if the state has changed, increment the counter
    if (servo1State == HIGH) {
      tankservo.write(open);
    }
      else {
      // if the current state is LOW then the button went from on to off:
      tankservo.write(close);
      
      }

        lastservo1State = servo1State;
}
}