What is the difference between SK protocol and SD protocol on the 5820XL, and can they be mixed?

The 5820XL supports either SK protocol or SD protocol, but they cannot be mixed on the same system (Page 91) [6].

SK devices use rotary dials for addressing and allow detectors and modules to share address numbers 1-99, supporting a total system capacity of 792 points (396 detectors and 396 modules) (Page 98) [1], (Page 73) [6].

In contrast, SD devices use EEprom addressing with unique addresses 1-127 for all devices and support a maximum of 508 total points (Page 98) [1], (Page 73) [6].