Reading Bits/Bytes Of A Word

[Scada_Newbie]

Hi All,

Just a question that is PLC and SCADA related.

I am using Wonderwares Intouch 9.5 and a Siemens S7-300 PLC, i have a word that stores a value in the lower byte and i will eventually add a value to store data in the upper byte of the word.

Thats ok, but how do i show this on my scada screen? I know i can see the individual bits of the word:

e.g. MyTag has an address of: DB89,INT36 (And Its Value is 1)

MyTag.00 = 1
MyTag.01 = 0
MyTag.02 = 0
'
'
MyTag.31 = 0
​

But if i want to know the lower and upper bytes(not the single bits), how would i do this?

Any help would be much apppreciated,

Many Thanks In Advance

 

[rdrast]

Read the whole word, and mask off parts of it?
High byte of a word (using integer math) is WORD / 256.
The low byte is then WORD - HIBYTE*256

If WW supports, you can also get the low byte by masking off the top:
LOBYTE = WORD & 0x00FF

 

[Scada_Newbie]

Bytes In A Words

Sorry, this is my problem.

i do not know if it is possible to read the lower & upper bytes in intouch.

When looking at MyTag Still with an address of DB89,INT36 in intouch it will show a 1 (For Example), what i need to do is find a way to find the value of the two bytes(upper/lower)

Any ideas ?

 

[krk]

The easiest way to do what you require is to create a couple of new tags in InTouch addressed with the bytes you're using...there are 2 methods of addressing byte variable tags, for the example you give in your first post, these would be

LH/MSB:
DB89,B36 or DB89,BYTE36

RH/LSB:
DB89,B37 or DB89,BYTE37

 

[parky]

There are a number of ways, as suggested, if the driver allows bit access then read them as bits/bytes or you can read the word as a tag, create internal tags & use simple maths to extract the words into bits/bytes.

Div by 256 etc or do it in a loop have a variable start at 1 and it with the word & if logical 1 (greater than 0 )then set an internal tag array bit(loop tag -1) to 1 else set it to 0, multiply the loop variable by 2 & run the loop until all 16 bits have been checked.

Some time since I used intouch, so not sure about the script required, I used this some years ago to convert 20 or so words into bits as the driver would not read bit values in data words.