Hi everyone,
I'm newbie in this forum, this is my first post, if I have any mistake, please help me to fix it! Thanks!
I'm writing new Modbus RTU library for arduino (master and slave) based on SimpleModbus. The reason why I create new library because I've tried to use SimpleModbus to communicate with my HMI screen but it reported a lot of errors.
- If I just send 1 packet, it's ok. But when I increase the packet, some errors appear.
- The polling time to work with library is too long, if I have 10 packets, and polling time is 100ms => 1 packet will be updated after 1 second.
I've tested with this library and it work well.
As you can see in the video. the transfer rate is about 38 packets/second => cycle time is 1/38 ~ 26.32ms. So if I have 10 packets, update time for each packet is 263,2ms without any error.
Note that the program above runs with rtos, the cycle time (polling) is only 21ms, but the transfer rate is 38 packets/sec. If I use polling by arduino loop, with polling = 21ms, transfer rate is only 23 packets/sec
When using polling by arduino loop, transfer rate can be smaller than 23packets/sec depend on your program, if you run a lot of code, the transfer rate will be decreased. polling can be as short as 2ms, transfer rate will be 40packets/sec (not better than using rtos 21ms~38packets/sec)
The library is worked with both arduino AVR and ARM, it does not require two separate library.
I'm going to put Modbus master and slave in same library. It will be easier to use.
You can download library at github:
Youtube video:
Thanks you.
(and I'm sorry about my english 
)
Example code:
#include "ModbusXT.h"
#define TIMEOUT 500 //Timeout for a failed packet. Timeout need to larger than polling
#define POLLING 20 //Wait time for next request . Unit in ms
#define BAUD 57600
#define RETRIES 10 //How many time to re-request packet frome slave if request is failed
#define BYTE_FORMAT SERIAL_8E1
#define TxEnablePin 2 //Arduino pin to enable transmission
#define print(x) Serial.print(x)
#define println(x) Serial.println(x)
//Name for register in regs[]
enum {
button1,
button2,
button3,
number_entry,
password_entry,
slider,
total_packets,
total_requests,
total_failed,
transfer_rate,
transfer_delay,
led_grn,
led_blue,
led_red,
graph,
TOTAL_REGS //=15
};
// This is the easiest way to create new packets
// Add as many as you want. TOTAL_NO_OF_PACKETS
// is automatically updated.
enum {
PACKET1,
PACKET2,
NO_OF_PACKET //=2
};
// Masters register array
uint16_t regs[TOTAL_REGS];
//Modbus packet
Packet packets[NO_OF_PACKET];
// Access individual packet parameter. Uncomment it if you know what you're doing
// packetPointer packet1 = &packets[PACKET1];
// packetPointer packet2 = &packets[PACKET2];
int graph_value = 0;
int slider_value = 0;
long sm,em,dm;
const uint8_t hmiID = 1; //ID of HMI. The ID need to match, unless program will not work
uint16_t temp,num;
//Modbus Master class define
Modbus master;
void setup()
{
//Config packets and register
master.configure(packets, NO_OF_PACKET, regs);
//Config individual packet: (packet, ID, Function, Address, Number of register or data, start register in master register array)
master.construct(&packets[PACKET1], hmiID, READ_HOLDING_REGISTERS, 0, 6, 0);
master.construct(&packets[PACKET2], hmiID, PRESET_MULTIPLE_REGISTERS, 100, 9, 6);
//Start Modbus
master.begin(&Serial1, BAUD, BYTE_FORMAT, TIMEOUT, POLLING, RETRIES, TxEnablePin);
Serial.begin(57600); //debug on serial0
println("Arduino Modbus Master");
pinMode(13, OUTPUT);
}
void loop()
{
master.update(); //polling
sm = millis();
graph_value++; //update graph data, just increase from -32768 to 32767 (signed int)
regs[total_packets] = NO_OF_PACKET; //Total number of packet, here is 2
regs[total_requests] = master.total_requests(); //Update all requested packets. Take a look on ModbusXT.h
regs[total_failed] = master.total_failed(); //Update all failed packet
regs[graph] = graph_value; //Update graph value
//If button is press, turn on HMI's LED
for (uint8_t i=0;i<3;i++)
{
if (regs[i] == 1)
regs[i+11] = 1;
else
regs[i+11] = 0;
}
//If Led green is on (or button 0 = 1) turn on Led on arduino
if (regs[led_grn])
digitalWrite(13, HIGH);
else
digitalWrite(13, LOW);
//Print number value on HMI
if (num != regs[number_entry] )
{
num = regs[number_entry];
print("Number: ");
println(num);
}
//Print slider value on HMI
if (slider_value != regs[slider] )
{
slider_value = regs[slider];
print("Slider: ");
println(slider_value);
}
//update transfer rate and transfer delay
if ( (sm-dm) > 1000) //update 1s
{
dm = sm;
regs[transfer_rate] = regs[total_requests] - temp;
temp = regs[total_requests];
regs[transfer_delay] = (unsigned int) ((NO_OF_PACKET*100000UL)/regs[transfer_rate]);
}
}//end loop
