CAS Modbus Explorer
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CAS Modbus Explorer is a utility to discover Modbus devices on a Modus RTU network. If you dont know the connection settings or the device address then this is the utility for you. It tries all combinations of
You can discover devices on a RS485 network if you use a USB-485 converter that presents itself as a serial (COM) port to your computer. The application tries to read a single register. If it gets a response (even an exception response) then it reports that the device exists. The application opens the port with a combination of port parameters and then sends a message to the 1st device in the address range. If there is a reponse then it reports the device. If there is no response then the application moves on to the next address. Once all the addresses for a given port setting combination have been tried then the application moves onto the next application. You can select if a single or if mutliple devices must be found in whihc case the full address range is tested even if a device is found. In BURST mode, the application opens the port with a combination of settings and then sends messages to all the devices in the specified range before wating for a response. In this way the 'timeout' for each address is bypassed and the search is speeded up significantly. A log is provided which reports the combinations attempted and the devices found. Features:
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Step 1: Select a COM port
Step 2: Select a Function Code and Offset Function 1 = Read Coil - 0xxxx Function 2 = Read (binary) Input - 1xxxx Function 3 = Read Holding Register - 4xxxx Function 4 = Read Input Register - 3xxxx Offset = 1 Means the 1st item. Thus, for example, Function 3 offset 10 means 40011 (the 10th 4xxxx register). Normally you can ignore this step and try anyway. The way we discover a device is by sending a message to read data from the device. The question is what data ? You see some devices dont respond if you poll for a data point that doesnt exist and some devices do respond by sending an exception response as the spec requires them to.
Most devices have holding resgisters but not all. So if the search fails then you need to try again using a different offset/function combination. We have seen thousands of Modbus devices and 80% contain 40001. We suggest you try the following Function=3 Offset=1 (Hold Reg 40001) Function=1 Offset-1 (Coil 00001) Function=2 Offset-1 (Input 10001) Function=3 Offset=100 (Hold Reg 40101) Function=3 Offset=1000 (Hold Reg 41001) The timeout is the amount of time in seconds that we will wait for a response. Some devices are slow. Two seconds should be safe. The larger the timeout the longer the discovery process.
Step 3: For RS232 select 'One Device' For RS485 select 'All Devices' Limiting the address range saves time but reduces the chance of finding the device. If your vendor has told you what the address is or if the address is obvious such as when it is set with a dip switch then limit the address range. Another Strategy is to seacrh address 1-32 then 33 ...
Step 4: Standard Mode - Sends a message and waits for a response Burst Mode - For a given port setting, sends messages to all devices in the address range and then waits for a response. This is a big time saver. This mode can only be used when searching for a single device. START the search.
Step 5: Interpret the results. Some devices dont check parity - they dont have to. In such cases you can expect the application to disover the device more than once. You send Odd and then even parity - it doesnt check so it responds.
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