screen /dev/cu.usbmodemfd411 115200
This is a very useful and little known command that sets up serial terminal. It turns out that it is necessary to first turn the device on. With a logic that only a hardware engineer can understand, the required command is called "*Zoff". If you do anything else initially, like trying the other commands in the documentation, nothing will happen. The "*Zoff" command also turns on all the little green LEDs on the device. Now everything will work as long as the accelerometer is run from the screen command.
The next step was to write my own program to communicate directly with the accelerometer. This turned out to be far from easy. After several hours with different strategies. I eventually realized that it was necessary to make a small pause between each character. By waiting 10 microseconds after writing each character, the communication would work more often. Making the delay longer does not seem to change the situation. This explains why everything worked when I was typing in the terminal emulator, but not from my program that would send out characters much faster.
The sad thing is that even with the delays, the communication is not reliable. Sometimes it works, sometimes it doesn't. So far I have not been able to figure out why, but I would say that this device would seriously need some handshaking. This will need to be systematically investigated. One more day to go.
