Contoh Master Modbus dengan Bascom AVR

berikut ini contoh master  modbus RTU  dengan menggunakan bascom avr
compiler bascom avr  menyediakan fungsi library untuk master modbus yaitu “modbus.lbx” dan fungsi  untuk mengirim query modbus :

MAKEMODBUS(alamat slave, fucntion code, alamat register, varbts )

function code yg tersedia

• 03 : read register

contoh

Slave Address                11
Function code                 03
alamat awal reg MSB    00
alamat awal reg  LSB      6B
jumlah reg MSB               00
jumlah reg LSB              03
CRC

• 06 : write single register
• 16 : write multiple register

$regfile = “m162def.dat”
$crystal = 8000000
$baud = 19200
$hwstack = 42
$swstack = 40
$framesize = 40

$lib “modbus.lbx”
Config Print1 = Portb.1 , Mode = Set

Rs485dir Alias Portb.1
Config Rs485dir = Output
Rs485dir = 0

Portc.0 = 1

‘The circuit from the help is used. See Using MAX485
‘ PB.1 data direction rs485

Config Com1 = Dummy , Synchrone = 0 , Parity = None , Stopbits = 1 , Databits = 8 , Clockpol = 0
Config Com2 = 9600 , Synchrone = 0 , Parity = Even , Stopbits = 1 , Databits = 8 , Clockpol = 0

Open “COM2:” For Binary As #1

Dim B As Byte
Dim W As Word
Dim L As Long

W = &H4567
L = &H12345678

Print “RS-485 MODBUS master”
Do
If Pinc.0 = 0 Then
Waitms 500
Print “send request to slave/server”
‘ Send one of the following three messages
‘ Print #1 , Makemodbus(2 , 3 , 8 , 2);
‘ Print #1 , Makemodbus(2 , 6 , 8 , W);
Print #1 , Makemodbus(2 , 16 , 8 , L);
End If
If Ischarwaiting(#1) <> 0 Then
B = Waitkey(#1)
Print Hex(b) ; “,”;
End If
Loop

End

sumber

http://avrhelp.mcselec.com/index.html?modbus_slaveserver.htm