User Manual

GM47/GM48 INTEGRATOR’S MANUAL

LZT 123 7263 R1A

2.17 Real Time Clock

The Real Time Clock provides the main microprocessor with a time-of-

day calendar and alarm, and a one-hundred-year calendar.

The Real Time Clock operates in two modes when connected to a

separate power supply:

• RTC normal mode: the module is in ON or OFF mode and it is

supplied with power (VCC is applied).

• RTC back-up mode: VCC is disconnected and the RTC is

maintained by a separate backup power supply connected to the

VRTC input (see Figure 2.7 below).

Backup power is provided by a capacitor, golden-capacitor or battery in

your application and must be connected to the VRTC pin. During RTC

normal operation, the back up source will be charged.

In back-up mode, the back-up source must provide enough power for

RTC operation. Refer to the table for the amount of current required.

The following table shows both voltage characteristics for both modes.

If the voltage drops below 1.0 V in back-up mode, the RTC will stop

working. The following diagram shows the RTC connections.

Figure 2.7 RTC connections

Pin Signal Dir Description

25 VRTC - VoltagefortheRealTimeClock

Parameter Min. Typ. Max. Units

Supply Voltage RTC (normal mode -

charging the capacitor)

1.6 1.8 2.0 V

Supply Voltage RTC (back-up mode -

Capacitor provides the current)

1.0 1.8 2.0 V

Current drawn 5.0 10.0 µA

Backup

supply

VRTC

GM47

DGND