Under sampled capture of startup. The top trace appears to be chip power supply. The data line appears to be shared by 3 chip and clock shared by all.

A trace which only shows the transients, all hi - flags no activity. This captures a complete sequence for one chip then shows power is dropped followed by a clock and no data.

The complete shut down sequence for all chips. Each chip appears to be accessed twice and the order is apparently different to the startup. Also note the power stays up the whole time.

A more detailed grab of the beginning of the shut down stream.