How to select the last elements in a string

[RuiZanzibar]

Hi Guys

I am using UART RS232 protocol and i need to calculate the check sum. My data came in decimal and in the end it must be doubles to manipulate it. So my problem is, for example, the sum of all elemants is in decimal 1742 and in hex is 6CE and i wont only the last two elemants, CE that corresponds to 206 that is the result of my checksum. Can anyone help me? 

Thanks

[jcarmody]

What is the data type you'll receive?  If it's acceptable to convert it to an I16 (or, if it is I16) this will work.

[Henrik_Volkers]

split number

edit: too late 😄

[RuiZanzibar]

Hello Jim and thanks for answer

My data came from an HMI device and in decimal. I'll show you an example:

123

123

160

54

111

103

110

108

107

109

108

108

100

100

100

100

0

0

1

4

5

0

0

0

0

0

0

7

96

1

0

0

0

0

0

10

51

1

0

0

51

1

1

23

12

0

206

125

125

The last third elemant is the Checksum. If i sum all the elemants from 160 (cmd) to the last cell before 206 (CKS) the result is 1742 (decimal) that correspond to 6CE has i told before, but is truncated to the 2 less significant digits CE that is 206. I will try the examples from you guys.

Thanks a lot                                                                                                                                                                                                                                     

[crossrulz]

I think this is what you are going for.  Your main issue is that you want to use String To Byte Array.  Each of those numbers are bytes.  To treat them as bytes instead of ASCII characters.

[syrpimp]

i dont know if it fits to your req. because my input is array just sum them up and convert to string...

crossrulz  i like your seminal coding

 

[RuiZanzibar]

Thanks Syrpimp

My data came from HMI in decimal like the example that i show above. Each cell is a value. You used an array, but i think that i can't use it because it must be done automatically and the data field have variable length. 

The UART protocol frame has a start frame field that corresponds to two ‘{‘ characters and an end frame field that corresponds to two ‘}’. Additionally, besides the data field, that has variable length, it has a byte that corresponds to the command type and another that is the checksum. The following table illustrates the protocol.

	Bytes considered in checksum
		Command Data
Start Frame	Cmd (hex)	Data0	Data1	Data2	Data3	Data4	Data5	Data6	Data…	CHK SUM	End Frame
{{										1 Byte CHK SUM (sum of all data bytes truncated to 1 byte)	}}

Fig. 1 UART communication protocol template

I receive data like this:

123

123

160

54

111

103

110

108

107

109

108

108

100

100

100

100

0

0

1

4

5

0

0

0

0

0

0

7

96

1

0

0

0

0

0

10

51

1

0

0

51

1

1

23

12

0

206

125

125

I'm trying explain my doubt the best way i can and i thank you all.

[crossrulz]

I highly recommend viewing your string in Hex display and change your numbers here into hexidecimal.  Things will make a lot more sense.  Then go look at my post above.  It does exactly what you are asking for.

[RuiZanzibar]

Hello again

I tried exactly has you told and the result isn't ok. See the attachment.

[crossrulz]

Your input data isn't correct.  I can tell because it should be starting with 7B7B and end with 7D7D.