Reading a timer seemingly not detecting tag structure

[maungawahau]

Hi,

I'm very new to python so forgive me if I'm on the wrong track. I'm just getting started reading tags from a CompactLogix L32E firmware version 20.19.

Here's the python 3.9 code I'm running within a venv in PyCharm 2020.3

from pycomm3 import LogixDriver
plc = LogixDriver('192.168.53.75')
plc.open()
print(plc.info)

print(plc.get_tag_info('AIR_MIXED_TMR'))

MyREAL = plc.read('HRS_HYDRAULICS')
print(MyREAL)

MyTimer = plc.read('AIR_MIXED_TMR')
print(MyTimer)

The read of a REAL tag works fine and I see the and see its value,

HRS_HYDRAULICS, 18678.357421875, REAL, None

However, when I try to read a standard TIMER, it does not appear to return the internal structure, the value is simply None

AIR_MIXED_TMR, None, None, Failed to parse reply - 

According to the PyCharm object browser, both MyREAL and MyTimer appear to be of a type Tag:4. Internally MyREAL has a value type of float but MyTimer has a value type of NoneType.

However, calling plc.get_tag_info('AIR_MIXED_TMR') indicates that the plc object is aware that AIR_MIXED_TMR has a timer structure

{'tag_name': 'AIR_MIXED_TMR', 'dim': 0, 'alias': False, 'instance_id': 64539, 'symbol_address': 396996, 'symbol_object_address': 1101252, 'software_control': 67221775, 'external_access': 'Read/Write', 'dimensions': [0, 0, 0], 'template_instance_id': 3971, 'data_type': {'name': 'TIMER', 'internal_tags': {'CTL': {'offset': 0, 'tag_type': 'atomic', 'data_type': 'DWORD', 'data_type_name': 'DWORD', 'array': 0, 'type_class': DWORD}, 'PRE': {'offset': 4, 'tag_type': 'atomic', 'data_type': 'DINT', 'data_type_name': 'DINT', 'array': 0, 'type_class': DINT}, 'ACC': {'offset': 8, 'tag_type': 'atomic', 'data_type': 'DINT', 'data_type_name': 'DINT', 'array': 0, 'type_class': DINT}, 'EN': {'offset': 3, 'tag_type': 'atomic', 'data_type': 'BOOL', 'data_type_name': 'BOOL', 'bit': 7, 'type_class': BOOL}, 'TT': {'offset': 3, 'tag_type': 'atomic', 'data_type': 'BOOL', 'data_type_name': 'BOOL', 'bit': 6, 'type_class': BOOL}, 'DN': {'offset': 3, 'tag_type': 'atomic', 'data_type': 'BOOL', 'data_type_name': 'BOOL', 'bit': 5, 'type_class': BOOL}}, 'attributes': ['CTL', 'PRE', 'ACC', 'EN', 'TT', 'DN'], 'template': {'object_definition_size': 24, 'structure_size': 12, 'member_count': 6, 'structure_handle': 3971}, '_struct_members': ([DWORD(name='CTL'), DINT(name='PRE'), DINT(name='ACC'), BOOL(name='EN'), BOOL(name='TT'), BOOL(name='DN')], {}), 'type_class': StructTag(DWORD(name='CTL'), DINT(name='PRE'), DINT(name='ACC'), BOOL(name='EN'), BOOL(name='TT'), BOOL(name='DN'), bool_members={}, host_members={}, struct_size=12)}, 'data_type_name': 'TIMER', 'tag_type': 'struct', 'type_class': StructTag(DWORD(name='CTL'), DINT(name='PRE'), DINT(name='ACC'), BOOL(name='EN'), BOOL(name='TT'), BOOL(name='DN'), bool_members={}, host_members={}, struct_size=12)}

I can successfully read the internal structure of the timer piece by piece. e.g
plc.read('AIR_MIXED_TMR.PRE')
plc.read('AIR_MIXED_TMR.ACC')

Is this behaviour normal or am I missing something? I had been under the impression that reading a TIMER tag by its basic tagname would return an object that replicated the structure of the timer, allowing members of that structure to be accessed without individually re-reading the tag piece by piece.

I'm grateful for your time,
Cheers,
Simon

[ottowayi]

So this is definitely a bug that I must've introduced recently, you should be able to read/write entire structures including the builtin types. You can see in the type_class=StructTag(... that the bool_members and host_members are empty, meaning DN/ACC/etc bits are not mapped to the CTL host member, so it tries parsing extra values when it should be mapping them. The builtin types are a handled a little differently than UDTs/AOIs, but to the user they should function exactly the same. But, I am noticing a pretty glaring omission in my tests, there's none that use any builtin types. I recently re-did all the tests and completely forgot to include those. Unfortunately, I am away on vacation right now and won't be able to get it fixed until probably the end of the week or this weekend.

[ottowayi]

I just pushed an initial fix to the develop branch. I have a few more things to do before I'm ready to put out a new release, but if you want to try it out beforehand it's there.

[ottowayi]

This is fixed in the latest release, v1.1.1

[danfly09]

I haven't tried this library yet, but after reading the homepage it seems that the read and write methods are not recommended for working with built-in types such as timers and counters. I'd like to confirm that this is still the case and if not, what will be then the recommended way to work with these types of tags? Thank you.

[dhunt84971]

You should be able to read and write to the individual components of these tags. For example, you can read the accumulated value from the timer T4:0 by reading the tag value for T4:0.ACC. To get the done bit status, read T4:0.DN, and so on.

Hope this helps.