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issue modbus connecting PDPM277H
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This answer was originally posted on DCIM Support by Balaraman Jagadeesan on 2020-01-21
Dear Miguel,
Yes, you are correct that the Modbus Over TCP is not supported in NMC1 brain. Modbus Over TCP is supported in NMC2 brain as per this link.
Based on my field experience, I did successfully configure the Modbus RTU in PDPM277H by using the Serial RS232.
Did you try to check the Modbus communication directly by using 940-0024 cable from your laptop? This can help you to understand if the issue is due to Modbus RS232 to RS485 converter or the NMC1 modbus communication.
You can use RS232 to communicate via Modscan software by using the serial cable (940-0024)
8 data bits, no parity, and one stop bit are fixed settings and not configurable for the PDPM277H. Please set the slave ID on the power view display.
You can use software like Modscan32 to check from your laptop. Here is the screen shot of the Modscan polling that I captured in the past from one of the customer sites.
Modbus Register map is available here.
Voltage:
As per the Screen shots, you can see that Modbus Register Map values are matching up with real readings for Voltage as shown below.
For Current readings, you can see that the real value is matching up if you refer the modbus register value offset by 1. For example: Refer the below screen shot below.
The Current value of Circuit 5a is 0.8 A. As per the modbus register map, Circuit 5a modbus register address is 2048. The modscan result shows the values correctly if the modbus register map 2048(i.e., offset by 1=20149)
Power:
Please see Power readings. The modscan result shows the values correctly if the modbus register map offset by 1=2121.
Timeouts
For each register, 500ms is recommended. Each Modbus register read causes the card to poll the device for that piece
of data and therefore, the timeout needs to scale with the number of registers polled per request. To allow for
unforseen circumstances, it is suggested to use the following equation to calculate the timeout: 500 ms * (number of
registers) + 100 ms = Total Timeout
It is recommended to poll blocks of 10 supported registers (or less that supports) at a time.
Scan Rates
It is suggested to configure your scan rate no less than 1000ms. Please keep in mind this setting may still need to be
adjusted depending on the number of devices, size of your queries, and the length of the serial bus.
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