Hi, all

This is my first post but i've scoured the forum many times in search of useful advice and often found it. This time though I couldn't find similar topics dealing with the particular problem I'm having so I'll ask the forum directly since you all seem so insightful.

Here goes...

I'm setting up PtP-network with with a remote controller that only supports communication over ASCII-protocol RS-485 (9600 baud, data bits 8, no parity, stopbit =1). I'm using a IM1517-CPU with a 1SI 138-4DF01-ASCII-module

Sending and receiving is isn't a problem with the gear itself but the remote "Net Controller" as it's called keeps sending back an error code saying it didn't understand the command.

Their customer support suggested i implement a short delay between the characters in the data stream as the microcontroller might need a short pause. "Fine", I said. I can program something to solve that...only i can't (see attachments). 

Since I'll have to send each character one by one, with a short delay in between, and TIA doesn't allow the character - '$'- I'll have to come up with a another way.

Funny thing is that when the full command - $01T0411<CR> - is inserted TIA doesn't complain. 

any ideas?

Hello,

this is why I don't use strings in my communications, but of course is choice of everyone. If I think that you can use in strings character $, it means that after this control character must continue hex representation of needed character. In case you want send only $ I see probably simple solution put inside this sequence - '$24', this mean hex 24 and this is $ as character representation. Also I expect better construct frame as Array of char where you can then define my sugested system, better Array of byte.

Thanks :)

I'm looking at the command being sent from the ASCII-module on my laptop and it looks much better when being sent from an array of bytes. I don't know why that is, though 

I think i might be able to pull this off

Hello,

as I said with that array of bytes, everytime use this. But also what Kaulquappe mentioned, it's strange that other side gives you this request, simply I don't know other side device but there are lot of solution how to set receive conditions. Question is what is that device.

Kaulquappe

 

Kim86

Their customer support suggested i implement a short delay between the characters in the data stream as the microcontroller might need a short pause.

 

Hello Kim,

I wonder that some manufacturers try to „stretch“ technical definitions. Serial asynchronous communication is defined as follows: Using 1 stop bit means there should be at least a 1 bit gap before the next character starts, with 2 stop bits the gap should be 2 bits. There is NO exception for devices which are slow. So when you implement a serial asynchronous communication you must make sure, that all characters received with the used baud rate can be evaluated before the last bit of the next character is received. If you are not able to do that, you can’t release this baud rate. It’s intolerable that the customer support asked you to send with gaps between the characters, as there is no software which supports this with standard functions.

There are two possiblilities to give the communication partner more time to evaluate the received characters:
- use 2 stop bits
- use a lower baud rate

Whether this works you can only recognize with “try and error”. A lower baud rate, even if it is very small, would be the better solution than sending single characters.

Regards,
Kaulquappe

 I couldn't agree more. "Implement a short pause"? It's apparent that they put more thought in to making this system work with their supplied PC-software and that PLC:s are a bit of an afterthoought. Thanks for all the help, guys! :) You rock.

Hi Kim86,

Sending entire string of character will result in tremendous delay. So such encrypted messages are used. The special character is not mandatory at all. U can use normal numbers also.

The best way to assure healthy communication is using acknowledgement. I recommend the partner should respond with same data set which it has received eg. $100. Next data should be released after proper validating the previously sent data.Such scheme will not need any pause.