ModbusMaster.h

#ifndef SIMPLE_MODBUS_MASTER_H
#define SIMPLE_MODBUS_MASTER_H

/* 
   SimpleModbusMaster allows you to communicate
   to any slave using the Modbus RTU protocol.
  
   To communicate with a slave you need to create a 
   packet that will contain all the information
   required to communicate to the slave. There are 
   numerous counters for easy diagnostic.
   These are variables already implemented in a 
   packet. You can set and clear these variables
   as needed.
   
   There are general modbus information counters:
   requests - contains the total requests to a slave
   successful_requests - contains the total successful requests
   total_errors - contains the total errors as a sum
   timeout - contains the total time out errors
   incorrect_id_returned - contains the total incorrect id returned errors
   incorrect_function_returned - contains the total incorrect function returned errors
   incorrect_bytes_returned - contains the total incorrect bytes returned errors
   checksum_failed - contains the total checksum failed errors
   buffer_errors - contains the total buffer errors
  
   And there are modbus specific exception counters:
   illegal_function - contains the total illegal_function errors
   illegal_data_address - contains the total illegal_data_address errors
   illegal_data_value - contains the total illegal_data_value errors
   misc_exceptions - contains the total miscellaneous returned exceptions 
  
   And finally there is variable called "connection" that 
   at any given moment contains the current connection 
   status of the packet. If true then the connection is 
   active. If false then communication will be stopped
   on this packet untill the programmer sets the connections
   variable to true explicitly. The reason for this is 
   because of the time out involved in modbus communication.
   EACH faulty slave that's not communicating will slow down
   communication on the line with the time out value. E.g.
   Using a time out of 1500ms, if you have 10 slaves and 9 of them
   stops communicating the latency burden placed on communication
   will be 1500ms * 9 = 13,5 seconds!!!!
   
   In addition to this when all the packets are scanned and 
   all of them have a false connection a value is returned
   from modbus_port() to inform you something is wrong with 
   the port. This is most likely to happen when there is 
   something physically wrong with the RS485 line. 
   This is only for information. You have to explicitly set 
   each packets connection attribute to false. 
   Packets scanning and communication will automatically
   revert to normal.
   
   All the error checking, updating and communication multitasking
   takes place in the background!
  
   In general to communicate with to a slave using modbus
   RTU you will request information using the specific
   slave id, the function request, the starting address
   and lastly the number of registers to request.
   Function 3 & 16 are supported. In addition to
   this broadcasting (id = 0) is supported for function 16.
   Constants are provided for:
   Function 3 -  READ_HOLDING_REGISTERS 
   Function 16 - PRESET_MULTIPLE_REGISTERS 
   
   Note:  
   The Arduino serial ring buffer is 128 bytes or 64 registers.
   Most of the time you will connect the arduino to a master via serial
   using a MAX485 or similar.
 
   In a function 3 request the master will attempt to read from your
   slave and since 5 bytes is already used for ID, FUNCTION, NO OF BYTES
   and two BYTES CRC the master can only request 122 bytes or 61 registers.
 
   In a function 16 request the master will attempt to write to your 
   slave and since a 9 bytes is already used for ID, FUNCTION, ADDRESS, 
   NO OF REGISTERS, NO OF BYTES and two BYTES CRC the master can only write
   118 bytes or 59 registers.
 
   Using the FTDI USB to Serial converter the maximum bytes you can send is limited 
   to its internal buffer which is 60 bytes or 30 unsigned int registers. 
 
   Thus:
 
   In a function 3 request the master will attempt to read from your
   slave and since 5 bytes is already used for ID, FUNCTION, NO OF BYTES
   and two BYTES CRC the master can only request 54 bytes or 27 registers.
 
   In a function 16 request the master will attempt to write to your 
   slave and since a 9 bytes is already used for ID, FUNCTION, ADDRESS, 
   NO OF REGISTERS, NO OF BYTES and two BYTES CRC the master can only write
   50 bytes or 25 registers.
 
   Since it is assumed that you will mostly use the Arduino to connect to a 
   master without using a USB to Serial converter the internal buffer is set
   the same as the Arduino Serial ring buffer which is 128 bytes.
*/

#include "Arduino.h"

#define READ_HOLDING_REGISTERS 3
#define PRESET_MULTIPLE_REGISTERS 16
#define WRITE_HOLDING_REGISTERS 6

typedef struct
{
  // specific packet info
  unsigned char id;
  unsigned char function;
  unsigned int address;
  unsigned int no_of_registers; 
  unsigned int* register_array;
  
  // modbus information counters
  unsigned int requests;
  unsigned int successful_requests;
  unsigned long total_errors;
  unsigned int retries;
  unsigned int timeout;
  unsigned int incorrect_id_returned;
  unsigned int incorrect_function_returned;
  unsigned int incorrect_bytes_returned;
  unsigned int checksum_failed;
  unsigned int buffer_errors;
  
  // modbus specific exception counters
  unsigned int illegal_function;
  unsigned int illegal_data_address;
  unsigned int illegal_data_value;
  unsigned char misc_exceptions;
  
  // connection status of packet
  unsigned char connection; 
  
}Packet;

typedef Packet* packetPointer;

// function definitions
unsigned int modbus_update(Packet* packets);
void modbus_configure(long baud, unsigned int _timeout, unsigned int _polling, 
                      unsigned char _retry_count, unsigned char _TxEnablePin,
                      Packet* packets, unsigned int _total_no_of_packets);

#endif