Read byte to ascii characters

Ignition
1

I have a machine that is storing the part number in the plc from address DBB10 to DBB59. Each character is stored as a byte. I want to be able to convert to character and combine to create a single tag called Partno.
How could this be done?

2

To start with, you might wish to check out the following URL:


You might say that life ( in Hexadecimal ) starts at 41 (Capital A) or at 61 ( Again Hexadecimal ) lower case a. It would take a third significant number if you stored it in Decimal ( 0-127) which can be translated back to a letter at a time with a Basic Interpreter command CHR$(decimal number). With that in mind, you would then need to decide how to read the PLC ( preferably into the Gateway default Database ) then how to create and update your Tag “Partno” in a way that makes sense for the number of part numbers you expect to read at a given time. If you expect to have a great number of part numbers and descriptions to go with them, you may want to consider an external database. Now would be a great time to get a ‘lite’ version of a Database program ( they are commonly called SQLs for Structured Query Language ). Discrimination between home and commercial use appears to now be an issue for anything connected to Java and/or Oracle ( line of products )- others may follow.
As to Tag creation from a Database, the modules in Ignition can tell you better for your specific Ignition versions- yet the general Database information may not apply to newer versions(yet).

3

It would seem to me that the Siemens Driver should be able to take care of this directly. I am assuming Siemens, although you didn’t specify in your post, or what version of Ignition you are using.

Something like DBSTRING10.40 would be a string starting at DB10 and is 40 characters in length.

https://docs.inductiveautomation.com/display/DOC79/Siemens

4

This will only work if it's actually being stored as a String in the PLC. The S7 strings aren't just an arbitrary sequence of bytes, they are prefixed by 2 bytes indicating max and current length.

2 Likes
5

Gotcha. One more reason to dislike Siemens… lol

Then something like this may put you in the right direction:

# generate tag list
tagPath = '[default]path/to/the/tags/'
tagList = []

for i in range(10,60):
  tagList.append(tagPath+'DBB'+str(i))

# read tags in list
tagValues = system.tag.readAll(tagList)

stringOut = ''
for tag in tagValues:
  if tag.value == 0:
    break
  stringOut += chr(tag.value)
  
print stringOut
6

I am using Ingnition319 version 7.9.4. The bender is a Siemens PLC stored as a decimal. From address DB400.DBB10 to DB400.DBB59 (50 bytes) each byte is an ascii character right aligned.
Our part numbers are typically 11 characters in length so I created 15 OPC tags to each which I think is not the right way to do it. I can see the values right aligned (0,0,0,0,49,54,50,50,55,51,95,67,69,76,76)
Converted would be (162273_CELL). I was thinking I could convert to the character and then build a string with the tags in an expression but that doesn’t work.
FYI I am only about 1 week understanding of ignition.
Am I doing it in the right manner or should I use a script or some other way.Capture

7

Where would I do this? Scripts? how would I store the value together with the other tags I want to capture?

8

Okay, the questions are getting a further afield. let’s take care of the first bit.

I set up a similar folder and tag structure on my server. I also made one more tag in the same folder just called PartNo.

I would put this in a gateway timer script at whatever rate you want to run it.

# generate tag list
tagPath = '[default]Test/PartNumber'
tagList = []

for i in range(1,16):
  tagList.append(tagPath+'/PartNo_Char'+str(i))

# read all the tags
tagValues = system.tag.readAll(tagList)

stringIn=''

# read one character at a time until we get to a non-printable character
for tag in tagValues:
  if  32 < tag.value < 127:
    stringIn += chr(tag.value)
  else:
    break
    
# reverse the string
stringOut = stringIn[::-1]
 
# write to the tag   
system.tag.write(tagPath+'/PartNo', stringOut)

If I’m reading the rest of your post correctly, you would be looking at transaction groups.

If you are not already aware, we do have Inductive University available to us that has a lot of good information and videos.

https://www.inductiveuniversity.com

1 Like
9

A more ‘pythonic’ way, along with reading the tags in reverse order.

# generate tag list
tagPath = '[default]Test/PartNumber'
tagList = []

for i in range(15,0,-1):
  tagList.append(tagPath+'/PartNo_Char'+str(i))

# read all the tags
tagValues = system.tag.readAll(tagList)

stringOut = ''.join(chr(tag.value) for tag in tagValues if 32 <= tag.value < 127)

system.tag.write(tagPath+'/PartNo', stringOut)
1 Like
10

We should add chr and ord expression functions… :thinking:

7 Likes
11

So what result should I see with the script you sent? I have been going through the courses. they are vary helpful but I don’t know where to search for what I would like to so I just need to get through the course.
I appreciate the help.

12

Though I haven’t tested, the script @JordanCClark supplied ought to read your PartNumber tags and turn them into the single string you are looking for. Add a memory string tag in your PartNumber folder named “PartNo”, put the script in a gateway time script (see here), try it out, and let us know how it goes.

1 Like
13

Thanks guys! That did the trick I missed changing the path from test/partnumber to my folder structure.

3 Likes
14

I am having a different issue. one of my triggers for one of my machines is duplicating the entry every part. I have check the setup at it is set to trigger on the part number tag changing the same way I do on the other equipment which does not give me a duplicate. What could cause this to happen?

15

And two years later we did. You'll find char() and ordinal() expression functions in the nightlies now and in 8.1.8 when it comes out.

3 Likes