APPARATUS FOR DEFINED SWITCHING OF A MICROCOMPUTER TO STANDBY MODE

Abstract: A regulated supply (12) to a microcomputer (11) is switched from main power to a standby power by a control circuit (10) in response to a switch off by a control circuit (10) in respect to a switch off command and only after the computer has been reset. Preferably, the circuit element is an operational amplifier whose output is fed by a threshold circuit (C1, R4, R3) which delays switching of the power supply (12).

Description: Apparatus for Defined Switching of _a Microcomputer to Standby Mode The present invention relates to circuitr for switching a microcomputer to a standb mode once the microcomputer is in a defined state, normally a reset state . It is known that if one ishes to retain information in a random access memory (RAM) it is neces¬ sary to provide a standb power supply to the RAM even when an associated microcomputer is switched off. Care must be taken, however, to ensure that the information contained in the RAM is not corrupted when the computer is switched off as may happen should the computer be s itched off when in the middle of accessing a RAM. Various circuits have been proposed for achieving a control switch-over to standby supply for RAM. Unfortunately, many of these circuits utilise a number of components and occupy a relatively large amount of space. Until now, this has rendered them inappropriate for incorporation in hybrid devices such as are used for many circuit electronic equipment fitted to motor vehicles. It is an object of the present invention to provide circuitry for performing controlled switching power supply to a RAM. The present invention provides a power supply arrangement for a microcomputer comprising regulator means for supplying a regulated main voltage or a regu¬ lated standby voltage to a microcomputer, and a hvbrid circuit having a plurality of circuit elements connected to the regulator means and arranged to be connected to the microcomputer for producing a resetting signal to the microcomputer and switching the regulator means in response to the potential of the resetting signal characterised in that a circuit element of the hybrid circuit is connected to be responsive to the resetting signal to generate a control signal for switching the regulator means. The advantage of the above arrangement is that an existing circuit can be utilised without any re-design of the circuit itself. Features and advantages of the present inven- tion will become apparent from the following description of an embodiment thereof given by way of example with reference to the accompanying drawing which shows a circuit diagram of a control circuit for s itching a microcomputer to standby mode. The present invention is based on an existing IC circuit represented generally by the reference numeral 10 and which comprises a number of operational amplifiers and components of a "watchdog circuit". The construction of the circuit 10 and its operation will be described in detail later. Associated with circuit 10 is a microcomputer 11 supplied with power from a voltage regulator 12 which in turn is connected via the input terminal 13 to the battery of the vehicle. The voltage regulator 12 sup- plies two regulated voltages; a main regulated power supply from the V out terminal 12a during normal opera¬ tion and standby power supply from the terminal 12b. The standby power supply is used to retain information in RAM associated with the microcomputer 11. As is known, operation of the ignition switch connected to terminal 15 is detected and a signal supplied to an ON " input 12c which causes the voltage regulator to switch on or off . In the present embodiment, the terminal 15 connected to the ignition switch is connected to the terminal 12c of the voltage regulator via diodes D2 , D3 and resistor RA . The diode DI is also inserted in the connection between the terminal 13 and the main power supply to the regulator 12. The diodes DI and D2 are used as polarity reversal protection diodes. With the ignition switch in its on condition, a voltage signal is present on the terminal 15 and the voltage regulator is in its normal condition with power being supplied to the microcomputer 11 from the output terminal 12a. A signal is also present on the VE input of the circuit 10 via resistor R2 which is connected to the output of the diode D2. The input terminal VE is the non-inverted input of an operational amplifier whose output is taken from the terminal VA and fed to the input terminal KE of a further non-inverting operational amplifier having an open-collector output KA. The output KA is of high impedance and enables the watchdog circuit 10a and containing external components R6 , R7, C3. The watchdog circuit is supplied with a watchdog signal WD shown in broken line from the microcomputer 11 by means of which it monitors operation of the computer and provides a reset signal in the event of a malfunction. It also provides a resent signal in response to a change in potential at the input S. Thus a change in potential at the Input S is reflected by a change in output potential at the output R (reset) which is connected to the microcomputer 11. The watchdog circuit may be a monitoring circuit of the type described in U.S. 4512019. In normal operation, with the ignition switch closed, the potential at input S is high which means that the output at R is low and the microcomputer 11 is not reset. The level of the signal at output R is fed to the inverting input XE of a further operational amplifier whose output XA is connected via resistors R5 and R4 to the control terminal 12c of the voltage regulator 12. Diode D3 decouples the output Xa from the Input Ve. When the ignition switch is operated to switch it off, the voltage on terminal 15 disappears and after a capacitor C2 connected to the input terminal VE has discharged below a low triggering threshold, the output VA switches to a low potential which in turn switches the output KA to a low potential to turn off the watch¬ dog circuit by lowering the potential at input S. In turn, the output R goes high which resets the microcom¬ puter 11 and also provides a high potential input to the terminal XE. Because the amplifier connected between XE and XA is inverting, the potential at output XA goes low and this in turn causes the potential at 12c to drop to a low potential after a capacitor Cl connected thereto has discharged. A low potential at 12c causes a tran¬ sistor 22 to switch on thus removing voltage from the base of main transistor 23 and turning it off. This causes the voltage regulator to switch to provide a standby voltage on the terminal 12b to maintain the RAM. It will be appreciated that the above arrange¬ ment can be modified to cater .for different types of circuit 10. For example, the flip flop between termi- nals S and R could provide a non-inverted output which would result in a change for the amplifier connected between terminals XE and XA to be a non-inverting ampli¬ fier. Further, as indicated by the broken lines the microcontroller itself, by detecting a low voltage at VA, can provide the necessary signal to cause the cir-

Claims: CLAIMS 1. A power supply arrangement for a microcomputer comprising regulator means (12) for supplying a regu¬ lated main voltage or a regulated standby voltage to a microcomputer (11), and a IC circuit (10) having a plurality of circuit elements is connected to the micro¬ computer for producing a resetting signal to the micro¬ computer and switching the regulator means (12) in response to the potential of the resetting signal, characterised in that a circuit element of the hybrid circuit is connected to the regulator means and is arranged to generate a control signal for s itching the regulator means (12). 2. An arrangement according to claim 1, wherein the output of the circuit element of the IC circuit (10) is connected to a control input (12c) of the regulator means (12) via a threshold circuit (Cl, R , R3). 3. An arrangement according to claim 2, wherein the circuit element is an operational amplifier.

Inventors: HUESER KLAUS, HUESER, KLAUS
Applicants: BOSCH GMBH ROBERT, ROBERT BOSCH GMBH
Application year: 1988
Main classification: G06F1
IPC codes: G06F1