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String in SCL

5/28/2014 7:42 AM	Rate (0)
Dwayne Chou Posts: 21 Rating: (2)	Hello Siemens, I'm working on a research project for making communication between S7-1200 and Microcontroller. By now, I can transfer a character from S7-1200 to Microcontroller then put in the LCD display. Now I try to send a string from S7-1200. But I wonder which the terminate type of string in S7 PLC is, I mean it's the stringterminated by a nullcharacter '\0' or the others. I used TSEND function to send a string stored in DB to Ethernet port on my laptop then used WireShark to catch the packets. It sent my string completely as I received on WireShark. But on the microcontroller, the receive function (in C code), I used the null character '\0' to recognise the end of string so I need to know which terminate type of string for fixing my code. Thanks for your help.
Dwayne Chou Posts: 21 Rating: (2)
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5/28/2014 10:10 AM	Rate (3)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 4/15/2025 Posts: 1560 Rating: (540)	Strings in S7 are not null terminated like those in 'c'. They consist of a 2 byte header and then the ASCII data. The first byte is the maximum length of the string and the second byte is the actual length of the string. So for a 20 byte string that contains "Smiffy" the string data would be in hex:- 14,06,53,6D,69,66,66,79 So if you program wants to receive and decode the string data it should first check the second byte (the actual string length) and then copy the rest of the ASCII data from position 3 in the string.
	Last edited by: smiffy at: 5/28/2014 10:47 AM Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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This contribution was helpful to 4 thankful Users 0_Einstein Rudrani Dwayne Chou n00dels

5/28/2014 10:24 AM	Rate (0)
Dwayne Chou Posts: 21 Rating: (2)	Thanks for your fast response, I will try it and give the feedback soon.
Dwayne Chou Posts: 21 Rating: (2)
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5/28/2014 11:51 AM	Rate (0)
Dwayne Chou Posts: 21 Rating: (2)	It worked! Thank you verymuch, Smiffy!!! I used your name on my test :D
Dwayne Chou Posts: 21 Rating: (2)
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This contribution was helpful to 1 thankful Users smiffy

5/28/2014 12:00 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 4/15/2025 Posts: 1560 Rating: (540)	Great stuff. Pleased you have it working. I'm not worried about you using my name - there is no copyright on it
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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