Yes, this is still possible with a Duet 3. Once you attach every Duet via USB, it will show up as a serial port that you may use for sending codes one by one.
if you prefer a network connection, you could use Telnet, too.
You can query full namespaces via M409 K”sensors” F”d99vn”. The new object model will be documented soon.
First a boot screen and then Chromium + Duet Web Control. However, there is a wide range of different displays out there and some may require additional configuration steps before they can be used.
FAT or FAT32, one partition
AFAIR mode 1 turns off the heater once it reaches the threshold. In mode 2 it is turned off as long as the protect condition is met. No heater fault is generated in both cases, thus the print is not paused either. This heater protection system allows multiple sensors (even RH sensors) to be coupled to a single heater. Another use-case could be a the protection of a heater using a backup temperature sensor.
The last example in the M143 description already describes a valid demo of mode 2.