I have an ND-6021 Analog Input Module. It is an RS-485 device that can set a variable output voltage based on the command it receives. I am trying to make it works under a Linux Debian Stretch. I have been using minicom to see if it works properly, so I issued a read configuration command:
$012<CR>. The device answers with the message
! means it received correctly the command and the rest of the message explains how it is configured. As far as I understand, this means that the connection is set up properly and there are no hardware problems that hinder the communication.
Next step is to set the desired level of output voltage. I have connected to the device a digital voltmeter, so I can see the output voltage. I issue the command:
#0108.467<CR> and I should read on the voltmeter a value of 8.467 volts and the device should answer with
>, but the voltage stays at 0 and there is no answer from the device.
I have spent hours checking the syntax of the command and it is right, so I did another test. I connected the device to a Windows laptop and using termite I issued the very same commands. The reading configuration command (
$012<CR>) works and I got the same answer as in Linux, and now also the setting voltage command works: I got the
> answer from the device and the output voltage is set properly.
I am confused because my test shows that the communication and the hardware settings are ok, but clearly, there is something that is not working, but what?