Hello Matthias,
Thank you for asking very interesting questions.
When you change the CR0,CR1 bits the change takes effect immediately after the ongoing (current) conversion is completed.
Since saving power by talking to multiple TMP103 devices at different times is your concern I would recommend you to go for One-Shot mode.
In this mode the device returns to the shutdown state at the completion of the single conversion which is ideal for power saving. By performing One shot on various TMP103's at different times you can save power. But please also take into effect the power consumed due I2C bus communication. More info on this mode can be found at Page9 of the data sheet.
If you want to save power and also do continuous conversions, I can think of another great option. Its a little tricky but I think it works if 1. Your I2C bus speeds are high 100-400kHz 2. If you can add and control delay time in your Host controller. Perform the following steps precisely:
1. By writing to bits M0,M1 of Conversion rate register, enforce all 4 TMP103's to shut-down with minimum latency between each devices.
2. Now set the CR1,CR0 bits on every TMP103 at your desired speed (Remember M0,M1 are still in shut down)
3. Now Set some delays in your host code such that you set M1 to '1' after a certain "delta time" between each of your 4 TMP103's.
I think this trick will work..Good luck and let me know how it goes!
Best Regards,
Abhi