User Manual

GM47/48 Technical description

BA/SEM/MS 02:0004 Rev B

3.17 Real Time Clock

The Real Time Clock provides with a time-of-day calendar with alarm

and one hundred-year calendar to the main microprocessor.

The real time clock operates with a separate power supply. Therefore,

two modes of operation shall be distinguished:

RTC Normal operation: This is when the MS is powered, and it does

not take into account if the MS is in OFF, ON or SLEEP mode.

RTC Backup operation: This operation is performed when the MS is

not powered, VCC = 0V. In this case the RTC operation is maintained

by the backup power supply.

The backup power supply is a passive power supply, capacitor,

golden- capacitor, battery etc., which shall be connected outside the

MS to VRTC pin. During the RTC normal operation, the passive

power supply is being charged; this is like charging a capacitor.

In backup operation, the backup source provides with enough voltage

for RTC operations. Following table shows both voltage operations

characteristics.

Parameter Min. Typ. Max. Units

Supply Voltage RTC (Normal Operation –

Charging the capacitance)

1.6 1.8 2.0 V

Supply Voltage RTC (Backup Operation –

Capacitance provides with voltage)

1.0 1.8 2.0 V

In Back-up operation if the voltage drop below 1.0 Volts, the RTC

shall stop working. Following picture shows the RTC connection:

Figure 3.6 RTC connection

A typical value for this capacitor will be 0.16F, this will power the

RTC for approximately 6 hours.