The top board is grbl based and can drive a small machine that has a laser diode.
The second board is a laser driver. The laser would be four wire, +/- fan and laser
Top board is three wire direct to the laser. Gnd, 12v, a modulation signal.
So they both appear to drive a laser and not necessarily designed to talk to each other. Just looking at diagrams online so if anyone knows for sure please post.