read_area reading merkers from PLC about python-snap7 HOT 5 CLOSED

Hello Rick! It could be very well you are the first reading out merker bytes. It could be that that constant is missing. You could try to read the source of snap7 and see which value s7areamk should be.

Read array returns a byte array which you need to interpret / cast to a python data type. There are are many examples of that in the snap7 python library.

from python-snap7.

S7AreaMK is defined in snap7.snap7types.

You should import it first, so above your read_area you should put:

from snap7.snap7types import  S7AreaMK

from python-snap7.

Ok thx as soon if i have some spare time i will try this.

from python-snap7.

Hello Gijs i tried it, bu no luck probably i do something wrong this the function i use:

def test_MB_read():
global client
counter = 0
size = 2
start = 0
db = 0
data = bytearray(size)
while counter < 10:
counter = counter + 1
from snap7.snap7types import S7AreaMK
data = client.read_area(S7AreaMK,db , start, size)
print('counter ' + str(counter))
print(type(data))
print ''.join('{:02x}'.format(x) for x in data)
time.sleep(1)

output:

ERROR:snap7.common:CPU : Invalid Transport size
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/pibrella.py", line 285, in handle_callback
self.handle_pressed(self)
File "./example.py", line 82, in Sequence
test_MB_read()
File "./example.py", line 50, in test_MB_read
data = client.read_area(S7AreaMK,db , start, size)
File "/usr/local/lib/python2.7/dist-packages/snap7/client.py", line 185, in read_area
check_error(result, context="client")
File "/usr/local/lib/python2.7/dist-packages/snap7/common.py", line 65, in check_error
raise Snap7Exception(error)
snap7.snap7exceptions.Snap7Exception: CPU : Invalid Transport size

if i change the size to 1 , i get output:

counter 1
class 'snap7.client.c_byte_Array_1'
00
counter 2
class 'snap7.client.c_byte_Array_1'
00
counter 3
class 'snap7.client.c_byte_Array_1'
00

etc........

Gr.

from python-snap7.

Ik think you are trying read a merker BYTE!. which is just 1 byte long. so
the size should always be 1

the import statemetnt should be above all your other code.
The code you are writing now 10 times reads Merker byte 0 from db 0 , once
every second for 10 seconds. and it probably is just 1 byte :)
you should still convert te byte value, to someting pythonic.

go read the official snap7 documentation http://snap7.sourceforge.net/
it should have everything you need!

Stephan.

On Fri, Oct 17, 2014 at 9:27 AM, Dabbadoeber [email protected]
wrote:

Hello Gijs i tried it, bu no luck probably i do something wrong this the
function i use:

def test_MB_read():
global client
counter = 0
size = 2
start = 0
db = 0
data = bytearray(size)
while counter < 10:
counter = counter + 1
from snap7.snap7types import S7AreaMK
data = client.read_area(S7AreaMK,db , start, size)
print('counter ' + str(counter))
print(type(data))
print ''.join('{:02x}'.format(x) for x in data)
time.sleep(1)

output:

ERROR:snap7.common:CPU : Invalid Transport size
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/pibrella.py", line 285, in
handle_callback
self.handle_pressed(self)
File "./example.py", line 82, in Sequence
test_MB_read()
File "./example.py", line 50, in test_MB_read
data = client.read_area(S7AreaMK,db , start, size)
File "/usr/local/lib/python2.7/dist-packages/snap7/client.py", line 185,
in read_area
check_error(result, context="client")
File "/usr/local/lib/python2.7/dist-packages/snap7/common.py", line 65, in
check_error
raise Snap7Exception(error)
snap7.snap7exceptions.Snap7Exception: CPU : Invalid Transport size

if i change the size to 1 , i get output:

counter 1

00
counter 2

00
counter 3

00
counter 4

00
counter 5

00
counter 6

00
counter 7

00
counter 8

00
counter 9

00
counter 10

00

Gr.

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from python-snap7.