ASCII Commands Over RS485

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.