Writing a function for sending data bytes at different baud rate without closing the port?

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#include <windows.h>
#include <stdio.h>
#include <conio.h>

// INITIALISATION FOR 25MS LOW AND 25MS HIGH WITH PREDEFINED BAUDRATE OF 200 Bps,DATA 0XF0//

int main()
{
int _kbhit();
int _getch();
// Defining hexadecimal bytes//
int bytes_to_send[1];
bytes_to_send[0] = 0xF0;

int GetPressedKey()
{
int ret = 0;
if (_kbhit())
{
ret = _getch();
}
return ret;
}

// Declare variables and structures//
HANDLE hSerial;
DCB dcbSerialParams = {0};
COMMTIMEOUTS timeouts = {0};

// Open the available serial port number//
fprintf(stderr, "Opening serial port...");
hSerial = CreateFile(
"COM3", GENERIC_READ|GENERIC_WRITE, 0, NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL );
if (hSerial == INVALID_HANDLE_VALUE)
{
fprintf(stderr, "Error\n");
return 1;
}
else
fprintf(stderr, "OK\n");

// Set device parameters (10400 baud, 1 start bit,
// 1 stop bit, no parity)
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
if (GetCommState(hSerial, &dcbSerialParams) == 0)
{
fprintf(stderr, "Error getting device state\n");
CloseHandle(hSerial);
return 1;
}

dcbSerialParams.BaudRate = 200;
dcbSerialParams.ByteSize = 8;
dcbSerialParams.StopBits = ONESTOPBIT;
dcbSerialParams.Parity = NOPARITY;
if(SetCommState(hSerial, &dcbSerialParams) == 0)
{
fprintf(stderr, "Error setting device parameters\n");
CloseHandle(hSerial);
return 1;
}

// Set COM port timeout settings
timeouts.ReadIntervalTimeout = 50;
timeouts.ReadTotalTimeoutConstant = 50;
timeouts.ReadTotalTimeoutMultiplier = 10;
timeouts.WriteTotalTimeoutConstant = 50;
timeouts.WriteTotalTimeoutMultiplier = 10;
if(SetCommTimeouts(hSerial, &timeouts) == 0)
{
fprintf(stderr, "Error setting timeouts\n");
CloseHandle(hSerial);
return 1;
}

// Send specified text (remaining command line arguments)
DWORD bytes_written, total_bytes_written = 0;
fprintf(stderr, "sending bytes...");

while(1)
{

if (!WriteFile(hSerial, bytes_to_send, 1, &bytes_written, NULL))
break;
fprintf(stderr, "%d bytes written\n", bytes_written);
if (GetPressedKey())
break;
// Read data here

if (GetPressedKey())

break;
}

CloseHandle(hSerial);

if(!WriteFile(hSerial, bytes_to_send, 1, &bytes_written, NULL))
{
fprintf(stderr, "End of transmission\n");
CloseHandle(hSerial);
return 1;
}
fprintf(stderr, "%d bytes written\n", bytes_written);

// Close serial port
fprintf(stderr, "Closing serial port...");
if (CloseHandle(hSerial) == 0)
{
fprintf(stderr, "Error\n");
return 1;
}
fprintf(stderr, "OK\n");

// exit normally
return 0;
}

Posted 23-Mar-15 4:14am

vinod b v

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Comments

ZurdoDev 23-Mar-15 10:15am

Where are you stuck?

vinod b v 23-Mar-15 10:35am

I am not understanding the way how to do it. first part of code works as i want, but once i send 1 byte of data at certain baudrate, later i need to change baudrate and send some more bytes of data to talk to ECU

Sergey Alexandrovich Kryukov 23-Mar-15 10:26am

Why doing so?
—SA

vinod b v 23-Mar-15 10:32am

for initialisation purpose

Sergey Alexandrovich Kryukov 23-Mar-15 10:38am

Are you trying to negotiate boudrate by preliminary communication using some initial boudrate (matching or not?)?
Not sure it's possible in this way...
See also the comment by Jochen Arndt below.
—SA

Jochen Arndt 23-Mar-15 10:29am

It should be possible to call SetCommState again with different settings. But you should ensure that there are no data on the line when changing the settings (wait until all data has been send and received).

vinod b v 23-Mar-15 10:37am

Could you help me with this part of as n how can i call the Setcomm state, and send the bytes of data with different baud rate could you give me an example?

Jochen Arndt 23-Mar-15 10:41am

You are already calling SetCommState. Just call it again with a new DCB or your dcbSerialParams structure after changing the BaudRate member.

vinod b v 23-Mar-15 10:42am

yes i shall do it, thank you.

vinod b v 23-Mar-15 11:22am

Dear JOchen, is this write?

#include <windows.h>
#include <stdio.h>
#include <conio.h>

// INITIALISATION FOR 25MS LOW AND 25MS HIGH WITH PREDEFINED BAUDRATE OF 200 Bps,DATA 0XF0//

int main()
{
int _kbhit();
int _getch();
// Defining hexadecimal bytes to be sent a 200 bps//
int bytes_to_send[1];
bytes_to_send[0] = 0xF0;

// Bytes to be send at 10400 bps//
int databytes_send[5];
databytes_send[0] = 0x81;
databytes_send[1] = 0x11;
databytes_send[2] = 0xF1;
databytes_send[3] = 0x11;
databytes_send[4] = 0x04;

int GetPressedKey()
{
int ret = 0;
if (_kbhit())
{
ret = _getch();
}
return ret;
}

// Declare variables and structures//
HANDLE hSerial;
DCB dcbSerialParams = {0};
COMMTIMEOUTS timeouts = {0};

// Open the available serial port number//
fprintf(stderr, "Opening serial port...");
hSerial = CreateFile(
"COM3", GENERIC_READ|GENERIC_WRITE, 0, NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL );
if (hSerial == INVALID_HANDLE_VALUE)
{
fprintf(stderr, "Error\n");
return 1;
}
else
fprintf(stderr, "OK\n");

// Set device parameters (10400 baud, 1 start bit,
// 1 stop bit, no parity)
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
if (GetCommState(hSerial, &dcbSerialParams) == 0)
{
fprintf(stderr, "Error getting device state\n");
CloseHandle(hSerial);
return 1;
}

dcbSerialParams.BaudRate = 200;
dcbSerialParams.ByteSize = 8;
dcbSerialParams.StopBits = ONESTOPBIT;
dcbSerialParams.Parity = NOPARITY;
if(SetCommState(hSerial, &dcbSerialParams) == 0)
{
fprintf(stderr, "Error setting device parameters\n");
CloseHandle(hSerial);
return 1;
}
// Calling DCB again //
dcbSerialParams.BaudRate = 10400;
dcbSerialParams.ByteSize = 8;
dcbSerialParams.StopBits = ONESTOPBIT;
dcbSerialParams.Parity = NOPARITY;
if(SetCommState(hSerial, &dcbSerialParams) == 0)
{
fprintf(stderr, "Error setting device parameters\n");
CloseHandle(hSerial);
return 1;
}

// Set COM port timeout settings
timeouts.ReadIntervalTimeout = 50;
timeouts.ReadTotalTimeoutConstant = 50;
timeouts.ReadTotalTimeoutMultiplier = 10;
timeouts.WriteTotalTimeoutConstant = 50;
timeouts.WriteTotalTimeoutMultiplier = 10;
if(SetCommTimeouts(hSerial, &timeouts) == 0)
{
fprintf(stderr, "Error setting timeouts\n");
CloseHandle(hSerial);
return 1;
}

// Send specified text (remaining command line arguments)
DWORD bytes_written, total_bytes_written = 0;
fprintf(stderr, "sending bytes...");

//fprintf("%d%%d%d%d%d",bytes_to_send[0],bytes_to_send[1],bytes_to_send[2],bytes_to_send[3],bytes_to_send[4]);//

while(1)
{

if (!WriteFile(hSerial, bytes_to_send, 1, &bytes_written, NULL))
break;
fprintf(stderr, "%d bytes written\n", bytes_written);
if (GetPressedKey())
break;
// Read data here

if (!WriteFile(hSerial, databytes_send, 5, &bytes_written, NULL))
break;
fprintf(stderr, "%d bytes written\n", bytes_written);
if (GetPressedKey())
break;

if (GetPressedKey())

break;
}

CloseHandle(hSerial);

if(!WriteFile(hSerial, databytes_send, 6, &bytes_written, NULL))
{
fprintf(stderr, "End of transmission\n");
CloseHandle(hSerial);
return 1;
}
fprintf(stderr, "%d bytes written\n", bytes_written);

// Close serial port
fprintf(stderr, "Closing serial port...");
if (CloseHandle(hSerial) == 0)
{
fprintf(stderr, "Error\n");
return 1;
}
fprintf(stderr, "OK\n");

// exit normally
return 0;
}

Jochen Arndt 23-Mar-15 11:47am

"Is this write"
I don't know what you mean.

Posting large code blocks as comment is not good. It is hardly readable. Your above code would probably even not compile (function GetPressedKey inside main function) and contains errors (calling CloseHandle twice; first call before WriteFile).

Some tips for new questions:
Code is better readable when formatting it in questions.

When pasting code into a question, there should be a popup window from where you can select "As code". You can also edit it later using the green 'Improve question' link. Mark the code section and select the 'code' item above the edit window (some HTML knowledge is useful).

Also don't post too large code dumps. Try to post the relevant parts only. This increases the chances to get answers.

vinod b v 24-Mar-15 5:27am

Dear Jochen Arndt, How do i make that the data arent on the line when changing baudrate. As per your advice i inserted another block the dcbSerialParams structure. but when i run all the data are overlapping. COuld you please help me on this issue.

Jochen Arndt 24-Mar-15 5:38am

This can be only answered when knowing how your devices is communicating (when data are send and how many data are send).

When the device is answering upon data that has been send it is simple:
Wait until all data has been received after writing.

vinod b v 24-Mar-15 6:30am

i am using USB to serial Converter for OBD Diagnostics. And the problem occurs when i try to send the other set of bytes at higher baudrate, i am trying to intitialise with KWP2000 protocol

Jochen Arndt 24-Mar-15 7:10am

So it is an OBD USB converter? Than check if the manufacturer provides some documentation (library, example code).

But there should be no need to change the baud rate. The used rate depends on the one used by the interface in the car.

KWP2000 (or ISO 14230) is a protocol and is not related to baud rates.

vinod b v 24-Mar-15 7:44am

I want to first do a wakeup pattern before talking to ECU, so i am using fast intialisation which uses 10400bps, but if i send all data at once i dont find the required timing diagram in my oscilloscope.The requirement for KWP 2000 is as follows
It operates at 10400 Baud.
Initial state – Tidle .
Tlow for 25ms and Thigh for 25ms
Start communication request from Tester to ECU
Start communication response from ECU to Tester.
I am able to generate 25ms low and 25ms high, at 200bps. and when i change the baudrate at 10400 for rest of bytes it does behave strange. I tried i call a function for the second part.

Jochen Arndt 24-Mar-15 8:09am

First of all: I have never used ODB.

According to a short web research fast initialisation uses logic low for 1.8 seconds.

Communication is 1-wire (K-line). So you need a special adapter. That should support initialisation (or at least provide examples).

You should search the web for examples. E.g.: http://www.codeforge.com/s/0/obd

KarstenK 23-Mar-15 14:17pm

If you want to change the baud rate you got to close and open the port. Somehow can the maximal baudrate get fetched.

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