One more question, please tell me, can we use a maximum of 128 variables in the T3-LB controller or more? I mean the number of variables that will be visible in BACnet.
I am not at my desk just now but I believe you are correct, 128 is the maximum for now.
Maurice Duteau
The polling is added to a pool of network points which automatically get refreshed by the network points task. there is no manual control over the polling rate. Yet.
I see that this could be useful and we’ll be looking at letting you control the polling rate by program control soon.
Maurice Duteau
Greetings!
I have a new question: I get Modbus temperature value with a sign. When the temperature is greater than zero, the controller displays it correctly, but when the temperature is negative, the controller displays it in the form “65526”. I guess this is a conversion problem. Please tell me, how I can write in the program that the value of the Modbus variable should be signed?
Default value is unsigned, so have to ask customer conver it if the value is negative.
10 VAR1 = 65526
20 IF VAR1 > 32768 THEN VAR1 = VAR1 - 65536
Hi @chelsea, thanks for the answer, I succeeded.
Unfortunately, you did not answer my question about pauses in Modbus requests. I see that polling by the controller is unstable and this is bad. You probably don’t suspect this, because usually Modbus Slave devices do not display read errors. I see these errors in the emulator program, see video: https://youtu.be/H3B0p6gX5Pw
I don’t see your code in which the controller generates a request, but I believe that in the controller’s request the pauses equal to 3.5 characters required by the Modbus standard are not met.
See below for an example of Python code in which these pauses are implemented:
# Sleep to make sure 3.5 character times have passed
minimum_silent_period = _calculate_minimum_silent_period(self.serial.baudrate)
time_since_read = _now() - _latest_read_times.get(self.serial.port, 0)
if time_since_read < minimum_silent_period:
sleep_time = minimum_silent_period - time_since_read
if self.debug:
template = (
"Sleeping {:.2f} ms before sending. "
+ "Minimum silent period: {:.2f} ms, time since read: {:.2f} ms."
)
text = template.format(
sleep_time * _SECONDS_TO_MILLISECONDS,
minimum_silent_period * _SECONDS_TO_MILLISECONDS,
time_since_read * _SECONDS_TO_MILLISECONDS,
)
self._print_debug(text)
time.sleep(sleep_time)
def _calculate_minimum_silent_period(baudrate):
"""Calculate the silent period length between messages.
It should correspond to the time to send 3.5 characters.
Args:
baudrate (numerical): The baudrate for the serial port
Returns:
The number of seconds (float) that should pass between each message on the bus.
Raises:
ValueError, TypeError.
"""
# Avoid division by zero
_check_numerical(baudrate, minvalue=1, description="baudrate")
BITTIMES_PER_CHARACTERTIME = 11
MINIMUM_SILENT_CHARACTERTIMES = 3.5
MINIMUM_SILENT_TIME_SECONDS = 0.00175 # See Modbus standard
bittime = 1 / float(baudrate)
return max(
bittime * BITTIMES_PER_CHARACTERTIME * MINIMUM_SILENT_CHARACTERTIMES,
MINIMUM_SILENT_TIME_SECONDS,
)
I await your reply!
Hello!
@chelsea, @maurice, I’m sorry, but I’m used to that when asking questions they have to answer.
Please tell me, do not you think so? Or do you intentionally ignore my question and believe that the problem does not exist?
I got a few more questions on less significant issues than stability on Modbus, but I can’t ask you them until I get an answer from you to an already asked question.
Hi @maurice,
I wrote all in detail in the message:
https://forums.temcocontrols.com/t/temco-plc-as-modbus-master/566/10?u=aleksei
and added in the message:
https://forums.temcocontrols.com/t/temco-plc-as-modbus-master/566/17?u=aleksei
UPD:
Probably the reason for the unstable operation of Modbus is not so much in the pause between requests, but in the structure of the requests themselves. Watch the video: Temco Modbus Polling Problem - YouTube
I made the same request to the Modbus register from the “Modbus Poll” program and from the T3-LB controller. Requests from the Temco controller come in torn form, unlike requests from Modbus Poll. Do you see this problem? Please tell me, can it be solved programmatically or is it a hardware problem?
There is a modbus delay parameter in some of our products, please check around in the T3000 user interface for it, advanced parameters tab. If its not in there for the T3-LB we can add it. I have asked one of the team to check on this as well.
All right, I will ask one of the team to add the modbus delay parameter to the T3-LB series
Hi @maurice,
today I did an experiment with one of my WAGO controllers and set up a poll of one Modbus register on TCP on it and similarly set up a poll on T3-LB, look what came of it: Temco T3-LB Modbus Polling Problem - YouTube
You see that the problem of T3-LB is not only in the pause between requests, but in a chaotic data stream. Is it fixable programmatically? If so, how long will it take?
Would you mind to use wireshark and send on the capture of this same test. We can work better from that than the movie.
Could I request a wireshark capture once again Aleksei, it will be much more clear for our engineers. Plus youtube is blocked in China.
Maurice
Hi @maurice , I did not know that YouTube is blocked in China. Tomorrow I will prepare the data you need.
Hi @maurice,
I looked at Wireshark, it does not suit us. The problem is that it does not work with COM ports (RS -232/485), only with Ethernet. In our case, the Temco controller is a Modbus master, which polls the slaves via RS-485. I suggest you use the DUNOVO SerialMon program, the trial version is available for download at https://www.dunovo.com/
To this message I attach a pdf file with a description of the problem and three log files for your analysis in the DUNOVO SerialMon program.
Modbus_Polling_Experiments.pdf (1.1 MB)
T3-LB_20191122.mon (10.8 KB)
Modbus_Poll_20191122.mon (2.1 KB)
WAGO_750-881_20191122.mon (3.1 KB)
I hope you can quickly respond to my message.
Thanks.
I didnt realize you are using Modbus over com port, we have some tools for that and will study what is going on here.
I checked the pdf file and use same capture tool to test, but did not find same issue. It is a basic freature as modbus master. it always woks well. Maybe you can give use more clues.
Hi @chelsea,
Hallelujah!
The problem of instability on the Modbus poll was in setting the RS-485/USB adapter. My adapter uses the Prolific chip in the settings which by default was set to “Low Latency Mode: 50,000 bps and less.” When I disabled this option the data transfer has started to work as it should.
Thank you very much for your check, which prompted me to this decision.
Good morning
I plan to test soon my first configuration with Nano controller and metzconnect triac output module on modbus
Basically to command the output, I would use MB_COIL command
Where can I find documentation about this.
Does it work on a Nano controller ?
Thanks for your feedback