Output:
Keyboard.Row9 is constantly held LOW during lightpen access
Keyboard.Row6 is constantly held HIGH floating during lightpen access(isn't HIGH because it's open collector)
Keyboard.Colums aka PSG.Ext.PortA are configured as inputs aka HIGH-Z
The above LOW and HIGH (or HIGH-Z) levels seem to be misused as power supply GND and 5V. There seems to be no power-supply required for the CPC version (unlike the ZX Spectrum version, which connects to cassette EAR port, and which requires an external 9V battery).