User's Manual

GS1500M DATA SHEET
PRELIMINARY GAINSPAN CONFIDENTIAL PAGE 11 OF 43
2.2.5 Clock Circuitries
The GS1500M architecture uses a low-power oscillator (i.e. 32 kHz) to provide a minimal subset of
functions when the chip is in its low-power deep sleep mode, and a high-speed 44 MHz oscillator to
provide clock signals for the processors, bus, and interfaces during active operation. Intermediate modes
of operation, in which the 44 MHz oscillator is active but some modules are inactive, are obtained by
gating the clock signal to different subsystems. The Clock & Reset Controller, within the device, is
responsible for generation, selection and gating of the clocks used in the module to reduce power
consumption in various power states.
2.2.5.1 Real Time Clock (RTC)
2.2.5.2 Overview
To provide global time (and date) to the system, the GS1500M Chip is equipped with a low-power Real
Time Clock (RTC).
RTC key features include:
► 32.768 kHz crystal support.
► Two external alarm inputs to wake up the device.
► Two programmable periodic outputs (one for a DC/DC regulator and one for a sensor).
► Embedded 128x32 non-volatile (battery-powered) RAM.
► Embedded Power On Reset.
► Real Time Counter (48 bits; 46 bits effective).
An overview of RTC block diagram is shown in Figure 2-3. The RTC contains a low-power oscillator
that can use 32.768 kHz crystals. In normal operation the RTC is always powered up, even in the Power
Up state (see Figure 2-3).
Two programmable embedded alarm counters (wrap-around) are provided to enable periodic wake-up of
the remainder of the system, and one independent external component (typically a sensor). Two external
alarm inputs enable wake-up of the system on external events. The global times are recorded on each
external event and if the system is in the Power-ON state (see Figure 2-8), an interrupt is provided. The
RTC includes a Power-On Reset (POR) circuit, to eliminate the need for an external component. The
RTC contains low-leakage non-volatile (battery-powered) RAM, to enable storage of data that needs to
be preserved.
Total current consumption of the RTC in the worst case is typically less than 5 µA without data storage,
using the 32.768 kHz oscillator.