Monday, February 29, 2016

Raspberry Pi - Python Snap7 - Mapping and Reading Datablocks


import snap7.client
from snap7.snap7types import *
from snap7.util import *


class DBObject(object):
    pass


offsets = { "Bool":2,"Int": 2,"Real":4,"DInt":6,"String":256}

db=\
"""
Temperature Real 0.0
Cold Bool 4.0
RPis_to_Buy Int 6.0
Db_test_String String 8.0
"""

def DBRead(plc,db_num,length,dbitems):
    data = plc.read_area(areas['DB'],db_num,0,length)
    obj = DBObject()
    for item in dbitems:
        value = None
        offset = int(item['bytebit'].split('.')[0])

        if item['datatype']=='Real':
            value = get_real(data,offset)

        if item['datatype']=='Bool':
            bit =int(item['bytebit'].split('.')[1])
            value = get_bool(data,offset,bit)

        if item['datatype']=='Int':
            value = get_int(data, offset)

        if item['datatype']=='String':
            value = get_string(data, offset)

        obj.__setattr__(item['name'], value)

    return obj

def get_db_size(array,bytekey,datatypekey):
    seq,length = [x[bytekey] for x in array],[x[datatypekey] for x in array]
    idx = seq.index(max(seq))
    lastByte = int(max(seq).split('.')[0])+(offsets[length[idx]])
    return lastByte


if __name__ == "__main__":
    plc = snap7.client.Client()
    plc.connect('10.10.55.109',0,0)
    itemlist = filter(lambda a: a!='',db.split('\n'))
    deliminator='\t'
    items = [
        {
            "name":x.split(deliminator)[0],
            "datatype":x.split(deliminator)[1],
            "bytebit":x.split(deliminator)[2]
         } for x in itemlist
    ]
    #get length of datablock
    length = get_db_size(items,'bytebit','datatype')
    meh = DBRead(plc,10,length,items)
    print """
    Cold:\t\t\t{}
    Tempeature:\t\t{}
    RPis_to_Buy:\t{}
    Db_test_String:\t{}
    """.format(meh.Cold,meh.Temperature,meh.RPis_to_Buy,meh.Db_test_String)
    plc.disconnect();