MODBUS communication over pDDL900 Radio

I have a Safecore gas detector that I am trying to remote connect to my computer through a Microhard pDDL900 radio. The sensor communicates using the MODBUS protocol, which I am not familiar with, and I'm running into issues getting it to talk with the radio. I am going into the serial port of the radio and have it configured as it should be but I cant even get the serial port to open up. I can direct connect the sensor to my laptop through a TTL232 USB to serial adapter, I have then connected into my laptop to the radio but still not having any luck getting them to talk. I know the radios are setup to be able to communicate because I can use a different system without the MODBUS protocol and they talk without an issue. All I'm trying to do is get the data OFF the sensor board and transmitted to my computer to display the data.
ANY help would be greatly appreciated as I have never used this data protocol before and running into issues getting the data to be transmitted that need to be solved soon for a test we are going to be doing in two weeks.


Unfortunately I don't have much experience working with radios, but I can provide some general comments on Modbus RTU and the settings you've shown in your attachment that may help.

Modbus RTU uses a minimum of 3.5 character times to delimit each packet. Therefore, your "Character Timeout" setting should be changed from 1 to 4.

Also, if possible, you may want to try a slower baud rate, like 9600, to confirm proper communication before trying faster baud rates.
I didn't see any handshake controls on your setup. Most radios use handshaking? This could be why it works back to back but not on the radio. The modbus software may not be using it while the other test software is. I'm not sure that modbus has anything to do with the problem. Are you seeing any messaging make it across the radio? What are you actually polling function code, data, gould or daniel etc
So I'll admit I did miss the CTS# and RTS# when I made the serial cable, I've since put those lines in but still no communication across the lines and serial ports are not even opening up on the radio when I click connect in the MODBUS terminal given to me by the Safecore company. All I'm trying to get from the sensor is the data from the individual sensors on it, there are 6 in total on the one board.
Does your modbus master software even control handshaking? Maybe try a different modbus sim software to see if its a software issue. Do you have a manual for the radio? The rs232 pinout?
I was able to Google a manual for the pDDL900 here:

However, I could not find any information or manual for a Safecore gas detector, other than that it may be part of this Radius BZ1 Area Monitor:

Is this what you're referring to by the Safecore gas detector?

Do you have a manual or documentation for the Safecore gas detector that details it's serial port and Modbus registers?
I'm not too worried about the gas detector yet. To me it doesn't seem like a message is being sent out. Serial config is on 70 , 71. I would also check with a volt meter rts dtr they need to be low when you are trying to send a message. As I said I would find another sim software to connect with the laptop to see if its software or hardware related
To test the radio connection and communication, you could connect both radios to your laptop (using a USB to RS-232 adapter for each radio) and use Modbus software such as ModScan and ModSim (, as both of these have hardware handshaking settings.

I recommend that you first use a null modem cable between your USB to RS-232 adapters to confirm that ModScan and ModSim can communicate successfully to each other, then connect the radios.