Unable to use windows.h ReadFile correctly on COM port. WriteFile seems to work fine - c++

Question

I am trying to use the windows.h library to communicate through RS232 with a device (SCPI communication). I have looked at several tutorials and guides on how to set this up and think my code should work correctly. I am able to send data to the device using WriteFile. However, I am not able to receive any data using ReadFile (ReadFile generates no errors but the buffer size is 0). Here is my code:
#include <stdio.h>
#include <windows.h>
void main ()
{
// CreateFile
HANDLE rs232 = CreateFileA ("\\\\.\\COM1", GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0, 0);
if (rs232 == INVALID_HANDLE_VALUE)
{
printf ("fail CreateFile: %d\n", GetLastError ()); system ("pause"); return;
}
// Get & Set CommState
DCB port_configuration;
int err = GetCommState (rs232, &port_configuration);
if (err <= 0)
{
printf ("fail GetCommState: %d\n", GetLastError ()); CloseHandle (rs232); system ("pause"); return;
}
port_configuration.BaudRate = 19200;
port_configuration.ByteSize = 8;
port_configuration.Parity = 0;
port_configuration.StopBits = 0;
port_configuration.DCBlength = sizeof (port_configuration);
err = SetCommState (rs232, &port_configuration);
if (err <= 0)
{
printf ("fail SetCommState\n"); CloseHandle (rs232); system ("pause"); return;
}
// SetCommTimeouts
COMMTIMEOUTS timeout_configuration;
timeout_configuration.ReadIntervalTimeout = 1;// MAXDWORD;
timeout_configuration.ReadTotalTimeoutMultiplier = 1;// 0;
timeout_configuration.ReadTotalTimeoutConstant = 1;// 0;
timeout_configuration.WriteTotalTimeoutMultiplier = 1;// 0;
timeout_configuration.WriteTotalTimeoutConstant = 1;// 0;
err = SetCommTimeouts (rs232, &timeout_configuration);
if (err <= 0)
{
printf ("fail SetCommTimeouts: %d\n", GetLastError ()); CloseHandle (rs232); system ("pause"); return;
}
// WriteFile
DWORD buffer_size_w;
char buffer_w[128] = "*IDN?\n";
err = WriteFile (rs232, buffer_w, strlen (buffer_w), &buffer_size_w, 0);
if (err <= 0)
{
printf ("fail WriteFile: %d\n", GetLastError ()); CloseHandle (rs232); system ("pause"); return;
}
printf ("written %d characters: %s\n", buffer_size_w, buffer_w);
// ReadFile
for (int x = 0; x < 10; ++x)
{
DWORD buffer_size_r;
char buffer_r[128] = {0};
err = ReadFile (rs232, buffer_r, 128, &buffer_size_r, 0);
if (err <= 0)
{
printf ("fail ReadFile: %d\n", GetLastError ()); Sleep (250); continue;
}
printf ("read %d characters: %s\n", buffer_size_r, buffer_r);
Sleep (250);
}
CloseHandle (rs232);
system ("pause");
}
Here is some more information about my setup:
I am using Windows 7 x64 and Microsoft Visual Studio 2013
The project is compiled as a Win32 Console
I use a FTDI Chipi-X USB to COM port converter cable
I have tried connecting with a Newport Motion Controller and a Thorlabs Piezo Controller
Here are the things I have tried so far:
Update the drivers of the Chipi-X VCOM
Change the COMMTIMEOUTS to various different values as seen in guides online
Using a HyperTerminal I am able to fully communicate back and forth with the device. If I use my own program to send commands that request something of the device, such as "*IDN?\n", my own ReadFile would thus return nothing. However, when I connect the HyperTerminal again I can press ENTER to receive the requested information.
Change the buffer sizes using SetupComm()
Change the ReadFile buffer size to 1 byte at a time
Implement the OVERLAPPED method as explained in this guide: https://msdn.microsoft.com/en-us/library/ff802693.aspx. It gave exactly the same problem as the non-overlapped code above: The windows functions would not generate errors but the read buffer would stay empty.
I tried communicating with a different device, this was interesting: Again I was able to fully communicate back and forth using the HyperTerminal. Whenever I used my own program to send, I would always receive the exact string I sent back using ReadFile. And again the actual requested information could be retrieved by reconnecting the HyperTerminal.
It seems to me there is some problem with buffers but I don't know what. I am also not sure if it is expectable that the HyperTerminal is able to pick up requested information that was requested several seconds earlier through a different COM port connection. Presumably the problem is related to my coding since the HyperTerminal works fine, but I cannot seem to find what is wrong with my code if I compare it with other code I find online.
Can someone help me out here?
EDIT:
I have created a new CLR/C++ test application using the following example: https://msdn.microsoft.com/en-us/library/system.io.ports.serialport(v=vs.110).aspx. This again gives the exact same problem of not being able to receive requests.
I have tried a Roline USB to RS232 cable: HyperTerminal works and my programming does not. The underlying hardware or drivers are likely not the problem here.

Answer 1

I solved the issue:
I forgot to send the carriage return (\r) at the end of my commands. Apparently the devices I was testing with both were waiting for the combination \r\n before actually parsing the request.
Somehow by using the hyperterminal I would be able to append the \r\n to the current COM port output buffer and get results delayed like that.