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Switching mechanism for battery-backed Real Time Clock

IP.com Disclosure Number: IPCOM000019170D
Original Publication Date: 2003-Sep-03
Included in the Prior Art Database: 2003-Sep-03
Document File: 3 page(s) / 73K

Publishing Venue

IBM

Abstract

A common service processor design is required for use across the different server brands. A real time clock is used to time-stamp events, such as errors, that occur in the server. This real time clock function must continue to operate even when there is no power to the card. Different applications require either a high-accuracy, temperature-compensated oscillator or a low-power crystal. Since a single design must be used in both applications, the following switching mechanism properly chooses the correct implementation of either the temperature-compensated oscillator or crystal, and supplies power to the real time clock and to the integrated circuit.

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Switching mechanism for battery-backed Real Time Clock

      A common service processor design is required for use across the different server brands. A real time clock is used to time-stamp events such as errors that occur in the server. There is a need in some applications to use a high accuracy real time clock. This feature requires the use of a high-accuracy, temperature-compensated oscillator. However, other applications are cost sensitive and require use of a lower accuracy real time clock that consumes much less power.

    Because of the temperature compensation of the oscillator, a relatively large amount of current is required for operation. Since this real time clock function must continue to operate even when there is no power to the card, a battery is used. The battery life of the clock circuit feeding the real time clock function of the service processor depends on the amount of current consumer. Normally, this would not be a problem in some applications because they have redundant power supplies. This becomes a problem when power is turned off the server for extended periods of time, or when the card is stored as a field replaceable unit. Since the card must operate in the server when it is replaced, a circuit must be implemented to switch from the high power, high current consumption, temperature-compensated oscillator to a low power crystal to minimize the current drain from the power source when external power is not available. Also, the low-end applications do not have redundant power and rely on battery back-up to continue operation of the real time clock when the server loses power. These applications must always use the crystal. The following implementation selects either the temperature-compensated o...