How to break a string!!

[altenbach]

I don't think you need any "e", you just need to make sure that you only process complete pairs. Then simply retain the leftover string (e.g. in a shift register) for the next iteration and prepend it to the new string.

[roiht]

I'm facing the same problem still. I used both methods attached in GetXY.vi. My problem with serial read is sometiems when visa should read whole of packet x233y34 like that at once. It just reads x23 or x233 and dumps the y34 part. Idunno how it happens and hence it becomes a bit problematic.
Im attaching my whole vi...can you just go through the extreme right part of my vi in the while loop...where I'm doing serial Visa read and scan the data string....
Looking for help

[mikeporter]

So if you took the part that comes after the last "x" in one read and appended it to the beginning of the string you get from the next read, would you get a complete datapoint? If so, do that. If not, assume that you can't trust the validity of the first element and the last element of each read and delete them.

Mike...

[roiht]

Hi mike,
I'm unable to find a permanent solution to this problem
When I should receive a string of say x45y65 ... sometimes I get only x sometimes x34 or sometimes x3(when actually string is x34...) whereas sometimes I get full correct string x23y45. I'm wondering where the data gets lost.!!  and athe string indicator reads just a blank!
Can you help me figure it out...

[mikeporter]

Can you post a complete string showing the problem? Have you tried the experiment that I suggested in your last post?

Mike...

[roiht]

What you told in the last post doesnt happen...the data is just lost...
I mean when I read just x and when Visa does the read next time...data of previous iterations is lost and what I get is the new data. I mean position is lost and it just reads just 0,0.
like if Im supposed to get:
x23y34
x24y35
x25y36
x26y37
I get sometimes
x23y34              //correct
x                       //faulty
x25y36                       //correct one
x26y3          //faulty
x27y38                     //this is correct one
x28y39                 //correcct
x29           //faulty
---
i hope you got my problem...
Waiting for your reply

[altenbach]

There seems to be no easy way to tell with 100% certainty if data is faulty. Here you assume that each number is 2 digits, but in the earlier posts you also had 3 digit numbers.

x234y236x233y23x238y34

For example if you would get x234y23, you would have no good way of telling if it is correct (really x234y23) or incorrect ( really x234y236).

[johnsold]

Are you now saying that the serial port does not get all the data? If you keep a partial dataset from one read (45y6) and append the next read (8x32y61x) to it, do you get 45y68x32y61x?

An earlier post in the thread pointed out that you need to retain the residual partial strings after decoding the available complete x, y pairs until more bytes have been recieved.

This is a common problem with devices which do not terminate each message with a unique character. In fact for your format you will always have an incomplete data set or uncertainty that the last y value is complete unless you know the maximum number of characters a y value can have AND the last data point includes that number of charcters. For example x3y5 may be complete or it may be the first part of x3y54 or x3y547. You do not know until a timeout occurs or the next x arrives.

Lynn

[roiht]

Yeah, That's correct that has been the problem for me.
You mean to say after x23y45 I can pass an end character like e to make sure that data has been received fully?
like x23y56ex24y55e...keep reading from the visa till I receive an e  and than process the string x23y45e. This way I can set boundry for the data?
Will that be of any help?
Looking for reply

[johnsold]

Yes. If you have control over the protocol used by the sending device, that is the ideal solution. Put all received characters into a shift register in the order received. Search the string for a group of characters bounded by an x and an e. The string between, for example 34y56, is the complete data for one point. Remove the string representing the complete point, including the x and e characters from the shift register and repeat the search. If you get a string which starts with x but has no e, then you know it is not complete and you wait for more bytes from the serial port before converting to numbers.

Lynn