ASCII Commands Over RS485

[GeorgeDumitru]

@jan-reitinger Hi Jan, here is the code of the entire block:

#define COM_BAUDRATE 9600 //baudrate, e.g. 9600, 19200, 57600, 115200
#define COM_PARITY_NONE 0 //no parity
#define COM_PARITY_ODD  1  //odd parity
#define COM_PARITY_EVEN 2  //even parity

#define BUFFER_SIZE 20 // MAXIMUM NUMBER OF BYTES TO SEND
#define COMMAND_LENGTH_MAX 20 //maximum length of command

//Assigning parameters to variables, these variables are read-only;
string parameter(0) serialdevice;//serial device is defined by parameter p0 of the REXLANG Block (e.g. /dev/ttyS0 in Linux or COM1 in Windows)

//Assigning inputs to variables
bool input(0) IsGreenButtonSignalOn;
bool input(1) IsRedButtonSignalOn;
bool input(2) IsYellowButtonSignalOn;
bool input(3) IsProcedureStandardSignal;

//Assigning Variables to Outputs, these variables are WRITE-Only
bool output(0) IsDeviceReady;
bool output(1) IsDeviceInError;
bool output(2) IsDeviceRunning;
string output(3) ResponseFromDMX;
long output(14) DebugMessage;
long output(15) ConnectionStatus;

//Variables Declaration
const long cr = 13; 	  // (cr) is the termination character, carrige return (0Dh);
long hCom, s, receive;	  // Communication Handle
long buffer[BUFFER_SIZE]; // buffer for incoming data
long dataCount; 		  // Number of bytes sent
bool read = true;
string data[BUFFER_SIZE+1];
int status=0;
long a;

void HomeMotor(void){
	long readData[6];
	readData[0]='L';
	readData[1]='H';
	readData[2]='O';
	readData[3]='M';
	readData[4]='E';
	readData[5]='-';
	s=Send(hCom,readData,6);
	return;
}


void ClearError(void){
	a=Write(hCom,"@DMK01EO=1[CR]");
	if(a>0){
		DebugMessage=a;
	}
	else{
		DebugMessage=-1;
	}
}
void MoveTo1000(void){
	a=Write(hCom,"@01J+");
	if(a>0){
		DebugMessage=a;
		status=0;
	}
	else{
		DebugMessage=-1;
	}
}

//the init procedure is executed once when the REXLANG function block initializes
long init(void)
{
	/* PUT YOUR CODE HERE */
	hCom=-1;
	

	
	return 0;
}

//the main procedure is executed repeatedly (once in each sampling period)
long main(void)
{
	/* PUT YOUR CODE HERE */
	if(hCom<0)
	{
		hCom = OpenCom(serialdevice,COM_BAUDRATE,COM_PARITY_NONE); //Opening Serial Device
		ConnectionStatus=hCom;
	}	
	switch(status)
	{
		case 0:
			a=Write(hCom,"@00EO[CR]");
			if(a>0){
				status=1;
			}
			break;
		case 1:
			dataCount = Read(hCom, data,BUFFER_SIZE);
			if(dataCount>0){
				if(data=="1"){
					ResponseFromDMX="ON";
				}
				else{
					ResponseFromDMX="OFF";
				}
				status = 0;
			}
		default:
			break;

	}

	return 0;
}

//the exit procedure is executed once when the task is correctly terminated
// (system shutdown, downloading new control algorithm, etc.)
long exit(void)
{
	/* PUT YOUR CODE HERE */
	if(hCom>=0){
		Close(hCom);
	}
	return 0;
}

[Jan Reitinger]

@georgedumitru, I believe there's a mistake in the Write command. Instead of using the [CR], it should be the ASCII symbol "\r". My apologies for not thoroughly reading the controller manual. Furthermore, I'm considering putting the switch into an else statement:

long main(void)
{
	/* PUT YOUR CODE HERE */
	if(hCom<0)
	{
		hCom = OpenCom(serialdevice,COM_BAUDRATE,COM_PARITY_NONE); //Opening Serial Device
		ConnectionStatus=hCom;
	}
	else
	{	
		switch(status)
		{
			case 0:
				a=Write(hCom,"@00EO\r");
				if(a>0){
					status=1;
				}
				break;
			case 1:
				dataCount = Read(hCom, data,BUFFER_SIZE);
				if(dataCount>0){
					if(data=="1"){
						ResponseFromDMX="ON";
					}
					else{
						ResponseFromDMX="OFF";
					}
					status = 0;
				}
			default:
				break;

		}
	}

	return 0;
}

[GeorgeDumitru]

@jan-reitinger Hi Jan, sorry if I'm being difficult here, but I am just curious, I am receiving a string in the return message. How can i process that to have the string in the output of the block? I managed to get a response from the device, and as long as the response is a single byte, that works just fine, but I am struggling to get a string out of the buffer. Do you have any suggestions?

[Jan Reitinger]

@georgedumitru Hi George,
if you only need a control statement in the log, use Trace(1,data). If you want the string to output directly, this should work:

...
string output(3) outputstring;
...
outputstring = data;

Cheers,
Jan

[GeorgeDumitru]

@jan-reitinger said in ASCII Commands Over RS485:

trol statement in the log, use Trace(1,data). If you want the string to output directly, this should work:

That's what I thought, but every time I try to do that I get this as an error:

[Jan Reitinger]

@georgedumitru Could you post line 111 here or ideally the whole code again?

This minimal example works for me:

#define BUFFER_SIZE 20

string output(1) outputstring;

string data[BUFFER_SIZE+1];

long init(void)
{
	data = "hello there";
	return 0;
}

long main(void)
{
	Trace(1,data);
	outputstring = data;
	return 0;
}

long exit(void)
{
	return 0;
}

[GeorgeDumitru]

Can you please help me with a conversion? I need to interrogate the position of the stepper motor, they have an ascii command I can send to do that, but the response is a 28-bit number. Can you tell me what I can use to get that number from the buffer?

[Jan Reitinger]

@georgedumitru Hi,
When we refer to a 28-bit number, does this imply that the number is transmitted within 4 bytes? If that's the case, and the number is in floating-point format, you should use double buf2double(buf[,endian]) REXLANG function.

[GeorgeDumitru]

@jan-reitinger said in ASCII Commands Over RS485:

buf2double

Hi, the number is not in floating-point format, is actually an int. But what I don't understand is how to use your function What exactly does it take in the argument. I never seen a function taking anything like yours and if I call just double myDouble = buf2double(myBuffer) I expect 100.000 and I get -7.403 669 410 330E-171 . So, how exacttly do i solve this?

[Jan Reitinger]

@georgedumitru
Hello George,

It's challenging to give advice remotely when I can't see what's happening. The data might be in a different format than expected. Could you use Trace() to print the contents of the buffer and share it here?

[GeorgeDumitru]

@jan-reitinger can you direct me to some documentation that shows how to actually use Trace() as I could definitely use that for myself too.

[Jan Reitinger]

@georgedumitru I think the best documentation is this thread here on the forum. Byte array reading from communication is also discussed there.

Another helpful tool is definitely the example located at C:\Program Files\REX Controls\REXYGEN 2.50.12.14711\Examples\0203_Function_Blocks_REXLANG.