Hi Bart,
I own a Powermax + with GSM module.
I've been reading on the PowerLink 'emulation' topics around the Visonic domoticaforum.
Tried to connect with Raspberry PI and Serial USB stick (FTD chip) and achieved to send some messages and to receive some (no real communication yet).
After this little test I found your application. At this point, I see the TX Led on the Serial port blinking when the tool is sending requests.
It just seems like my Powermax does not respond:

(There's a green RX Led on the port for visualizing reaction)
I've been trying to perform these actions when it is 'searching' Powerlink, but nothing seems to get 'm hooked up.
Now I'm not sure whether I missed something on these PIN-code / Download-code settings. I've changes te pin / cleared it and Download-code stated to default 'AAAA'.
Btw, when I call a python read-script, I do see the PowerMaster sending this enrollment code (like; 0xAB 0x0A 0x00 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x43) as described in Rene's protocol description.
You think there's anything I could try more to debug somehow?
Thanks in advance / kind regards,
Jeroen Janssen