PC to Arduino RS-485 connection via converters - arduino

Question

I'm trying to make modbus RS-485 connection between PC (Windows) and Arduino.
On the PC side I use USB-to-RS485 converter like this one http://ru.aliexpress.com/item/USB-to-485-RS485-converter-Adapter-Support-Windows-7-8-for-Arduino/1577970568.html
On the Arduino side I use TTL-to-RS-485 like this one http://ru.aliexpress.com/item/5pcs-lot-MAX485-Module-RS-485-TTL-to-RS485-Module-for-Arduino/32262338107.html
Problem1:
When I send byte from PC to Arduino. Nothing happens. Arduino does not receive anything. In this case i upload to Arduino this code:
#include <SoftwareSerial.h>
#include "RS485_protocol.h"
SoftwareSerial rs485 (10, 11); // receive pin, transmit pin
const byte ENABLE_PIN = 3;
void setup()
{
Serial.begin(9600);
rs485.begin (28800);
pinMode (ENABLE_PIN, OUTPUT); // driver output enable
}
void loop()
{
byte buf [1];
byte received = recvMsg (fAvailable, fRead, buf, sizeof (buf));
if (received)
{
Serial.println(buf[0]);
} else {
Serial.println("--");
}
} // end of loop
int fAvailable ()
{
return rs485.available ();
}
int fRead ()
{
return rs485.read ();
}
And open Serial Monitor in Arduino IDE to show received data.
Then I open new instance of Arduino IDE, chose proper USB-to-RS485 COM port and opens it Serial Monitor to send some data.
So in Arduino side Serial Monitor I see only "--" lines. Even when I'm trying to send something in PC side Serial Monitor.
The other problem is:
Vice versa. When i sending some byte from Arduino to PC I receive some odd symbols instead sent byte.
The Arduino code in this case is:
#include <SoftwareSerial.h>
#include "RS485_protocol.h"
SoftwareSerial rs485 (10, 11); // receive pin, transmit pin
const byte ENABLE_PIN = 3;
void setup()
{
rs485.begin (28800);
pinMode (ENABLE_PIN, OUTPUT); // driver output enable
}
void loop()
{
byte msg[1] = {3};
sendMsg(msg);
} // end of loop
void sendMsg(byte msg[])
{
delay (1); // give the master a moment to prepare to receive
digitalWrite (ENABLE_PIN, HIGH); // enable sending
sendMsg (fWrite, msg, 1);
digitalWrite (ENABLE_PIN, LOW); // disable sending
}
void fWrite (const byte what)
{
rs485.write (what);
}
int fAvailable ()
{
return rs485.available ();
}
On the PC side (in the Arduino IDEs Serial Monitor) I receive odd symbols instead "3" symbol.
=======
RS485 converters wired with twisted pare A to A and B to B.
RS485 to TTL converter connected to Arduino properly. (Communication between two arduinos works fine).
Please help.

Answer 1

Example of RS485 :
Using a SN75176 IC.
RE (pin 2) connect to ground (for always reading )
Arduino control only DE PIN for writing data
But PC side problems:
Where bridged DE pins ? (CTS,DTR,RTD if supported)
What is your flow control ? (related #1)
Did you connect any resistor to A, B pin ?<+5V>----[560R]-----(A)----[120R]-----(B)------[560R]------<-5V> So mean line end
Did you filter DE Pin 2 signal (for noise)
A tricks : Use SN75176 on arduino side because this IC a RS232(UART) to (RS485) converter.
Edit : Modbus got 2 type on serial (RTU, ASCII). Dont care RS232/485 differences because different signal, same protocol.
Example packet type:
ASCII : :010300200004+CRC+FE(crc =packet check code, fe=end delimeter)
RTU : \x01\x03\x00\x20\x00\x04\x +CRC
On rtu : every byte need 1.5 char space and without start and end delimeter.
And Modbus node type meaning master and slave.
I hope helpfull.