I have a Rigol DL3021 programmable load. I'd like to control it as part of an automated test setup, over SCPI from a Linux box.
Their programming manual assumes you're on a Windows machine and wants their software to be installed as a prerequisite. Luckily there's an open source VISA implementation called
pyvisa which I've had success with over USB. I'm able to detect the device and send it commands. On a side note it seems a bit finicky, but I am new to SCPI and it is perhaps my fault.
Regardless, if I could, I'd like to control it directly over RS232 with SCPI commands. I am ok with writing a small SCPI wrapper driver and giving up whatever nice abstractions VISA provides me in doing this. I have a RS232 to USB FTDI cable which is known working.
When I write SCPI commands to the serial device, though, nothing happens and I receive no response. I have checked the baud, parity, stop bits, control, many times and am confident they match. I see nothing in the manual about needing to explicitly enable RS232 communication on the device.
As an extra datapoint,
pyvisa documentation says it should pick up the device over the RS232 adapter, but it doesn't. I'm unsure what to make of this, I have no way to talk to it with the RS232.
This might be where I'm a bit lost, as I'm unclear if there's some handshaking or other magic that needs to be done to start communication with the load. I am working under the assumption that I can send it SCPI commands directly over the RS232 connection, but perhaps I've oversimplified this.
How do I connect to an instrument and check the serial connection?