Domain Messaging Display

Domains: Messaging (0x09) & Display (0x0A)

Messaging — not on Model 8810

Characters: uppercase alphanumeric (and spaces). Message center: 31 characters visual (16 top + 15 bottom). Protocol uses hex ASCII + null line terminators.

9.1 Permanent Messages

COS	No
Access	R/W
Read selector	Message number 0–3 as Read Request data

Byte	Field
0	Message number 0–3
…	Line 1: up to 16 chars + null
…	Line 2: up to 15 chars + null

• Writing two nulls only deletes the message.
• Thermostat cycles permanent messages; null messages skipped.

9.2 Temporary Message

COS	No
Access	R/W

Same character rules: top line + null, bottom line + null. Temporary message suspends permanent rotation until cleared with a two-null delete write.

10.1 LCD Backlight Settings

COS	When changed at thermostat
Access	R/W

Byte	Field	Values (summary)
0	Constant backlight / 8840 screensaver	0 Off/blank; 1 reserved / clock&temp (8840); 2 On / dim (8840)
1	Active backlight level	0–10 → Off…100% (steps of 10%; some levels N/A on 8840)

Note: with constant backlight, minimum active level is 40% on applicable models.