What is the maximum number of addressable devices the 6820 panel can support?

The basic 6820 panel contains one built-in signaling line circuit (SLC) which supports up to 159 SK sensors and 159 SK modules, or 127 SD SLC devices. Additional SLC expanders like the 6815 (supporting up to 159 SK sensors and 159 SK modules each) can be added for a maximum of 1,110 points per 6820 control panel, while the 5815XL supports SD Protocol devices only for a maximum of 635 points per panel. (Page 10)