Modbus "active source point has no value"
I created a new Modbus/TCP datasource with a 1-second update period, like many other Modbus datasources that are working fine. However, this new Modbus source reports "active source point has no value" for some datapoints, even though they worked when performing a "Point locator test" on the datasource page. On the graphical view, these points report "point value may not be reliable" and display "(n/a)" rather than a numerical value. The event page filled up with "Illegal data value" datasource alarms.
Why would the "Point locator test" work, but not the point it created?
Shouldn't the Modbus I/O log file report I/O originated from the Modbus read/write tools on the Datasource page?
The following is pasted from the Modules page:
core 2.8.8 build 635 - paid
modbus 1.8.0 - paid
JoelHaggar last edited by
I would suggest reducing the "Max read register count" value and/or checking the "Contiguous batches only" box. When you use the Point Locator tool it's just a single request but when you turn on the whole Data Source the default request might be too large for the device so you could get a partial response.
"Contigous batches only" solved the problem. Thanks.
Shouldn't the IO log file also log the individual read/write I/O operations (i.e. shouldn't it log ALL I/O)?
phildunlap last edited by
Yes it should have logged the IO.
Very likely there was a register that was requested based on the read register size settings coupled with your register spacing that was illegal, and you were seeing illegal data address, not value. "Contiguous batches only" will never request a register you haven't configured it to get data from, where otherwise it may request holding registers 0-150 (depending on your read settings) just to read 0 and 150. Let's say 75 is configured to be a private register, this would cause what you're seeing.
I also created a post about this, but i will make my request available (also) here.
I try to connect to an (external) modbus device, but after my system scanned it in my local networks, doesn't allow me to verify "next step" button and establish the connection.
phildunlap last edited by phildunlap
I responded in your thread, but I'm not sure I understand what you mean "verify next step button." Can you post a screenshot?