Real-time Clock (RTC) and Low-power Mode

The WM2000 features a real-time clock (RTC) and a dedicated RTC power input pin called "VCCB." The acceptable voltage range on this pin is 1.8V ~ VCC (which is 3.3V nominal). VCCB draws about 3µA (±15 percent depending on the configuration of the attached hardware).

For normal module operation, RTC power must be connected at all times. If there's no backup battery (supercapacitor), connect the VCCB pin to VCC. The VCCB pin draws power even when the WM2000 is active. Therefore, it is not an "RTC backup power input," but simply an "RTC power input." To prevent the backup battery (supercapacitor) from getting drained even when the main power is applied, use a simple "power selector" circuit as shown below.


Your Tibbo BASIC/C applications can access the RTC through the rtc. object, which is documented in the TIDE, TiOS, Tibbo BASIC, and Tibbo C Manual.

Low-power mode

By adding an external power switch controlled by the WM2000's LP line — as shown in the below diagram — you can allow the module to go into the low-power mode.

The LP line belongs to the RTC domain and remains operational for as long as there is backup power on the VCCB pin. During normal module operation, LP is HIGH, thus keeping the power switch turned on and the VCC line powered. Calling sys.sleep (see the TIDE, TiOS, Tibbo BASIC, and Tibbo C Manual) halts the module and causes LP to go LOW. The power switch then opens, and the power supply to the VCC pin is interrupted. The RTC continues to run, consuming only about 30µA from the backup power source.

The sys.sleep method defines the date and time for the module to wake up. When that moment is reached, the LP line goes high, and the WM2000 powers up.      

Note that "waking up" from the low-power state does not "resume" execution from the previous point but is instead a full reboot of the module.