Modbus RTU Modem

Hardware
1

I have two NCD enterprise 2ch 4-20ma current loop sensors turned on near the NCD enterprise Modbus RTU modem (white model). I am trying to poll the registers of the modem with my Modbus master device. The master device is set to 9600, 8N1, and attached is my Modbus master table. I read in the documentation I can poll 50 registers and always get the correct packet back, but my master continues to just time out. My request delay is 250ms, my response timeout is 1000ms.

How do I need to setup my table to poll registers from the NCD device?

2

modbus
modbus1920×1080 150 KB

3

I eliminated registers one by one to see if they would work and it does work with FLOAT data when reading 13 registers, but I do not know which registers are which.

3
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4

Ideally, you should be checking the data ready flag, and if it’s true than read the sensor data.

5

How would I check the data ready flag?

I would like to just read all available data based on some time interval I have on my Modbus master.

7

There is a data-ready reg in the Modbus modem. Checkout the manual.
so It will look like this

  1. check data ready flag after every 1min or so
  2. if flag it true then read sensor data
8

There is no manual online for the Modbus RTU Version

9

Is it not possible to check the specific registers of the device?

I only have 2 -2ch 4-20ma current loop devices, and will eventually have 3 more to add in the future. All I really care to know is battery life and each channel reading from the sensors.

10

use function code 3 and read 0-100 reg… it will always respond with the last received sensor data packet.