An electronic control system, as for instance a microcomputer in a microwave oven, is automatically reset when a signal, normally provided by the microcomputer within some normal interval relative to some reference, fails to occur. A reset command signal is generated and resets the microcomputer to some initial point from which normal operation may begin or resume and at which certain output loads may be rendered inoperative. A display device associated with the appliance is repetitively scanned at some normal interval and may provide the monitored signal. Circuitry capable of generating a reset-command signal is inhibited by the occurrence of a transition attending the display scan signal so long as it recurs within the particular interval. A timing capacitor is reset, as by being discharged, each time a transition attending a display scan signal occurs. If the capacitor is not reset, the voltage thereon ultimately attains a level which results in the generation of the reset command. Repetitive time-spaced reset commands may also be provided to insure success of the resetting operation. This reset command generating circuitry may be independent of and external to the microcomputer.
A timer which is resistive or substantially impervious to an outage which is encountered in the main power supply voltage. The timer includes a non-volatile power storage for specifiable switching timepoints, and instead of a power storage-buffered or backed running reserve possesses only a resetting device for the actual timer time setting at the renewed availability of the main power supply.
In a microprocessor controlled fire alarm system, a chain of continuous pulses is generated by the microprocessor. The chain of continuous pulses is monitored, and if there is an interruption in the chain of continuous pulses a signal is generated to automatically reset the microprocessor.
An IBM PC compatible keyboard is provided which, on power-up, does not access the keyboard LEDs until receiving a command from the host computer. When the keyboard controller performs a Basic Assurance Test (BAT) on power-up before receiving a host command, the controller does not turn on the LEDs. Upon receiving a Reset command from the host, the controller: (1) turns on the LEDs and performs a BAT with LEDs on; and (2) flashes the LEDs a second time to be compatible with the IBM PCs. Another feature of the invention is a non-destructive test of the controller RAM during BATs. The RAM is tested non-destructively both for the "stuck-at-1" and the "stuck-at-0" conditions. Still another feature is that the controller determines the state of the keyboard LEDs without reading a hardware port. The controller keeps track of the LED state by flags in the controller memory, and the controller determines the LED state by reading the flags.
A computer system is provided that allows a user to switch between at least two networks having different levels of security without transferring data between the two networks. The computer system comprises a standard computer which includes a central processing unit (CPU) coupled to a random access memory (RAM), a power supply and a reset switch. The computer is coupled to each of two different network cards, each of which is in turn connected to a separate storage device, such as a hard drive. Each combination of a network card connected to a storage device constitutes a network. As in a standard computer, activating the reset switch reboots the CPU and clears the RAM. A user chooses between the two networks by using a rotary switch, a rocker switch, or a push button switch which activates one of the networks or the reset switch. The switch is constructed so that it is impossible to switch between the two networks before first activating the reset switch, thereby preventing data from being transferred between the two networks. By preventing the transfer of data between the two networks, each of the systems can have a different level of security.
An IBM PC compatible keyboard is provided which, on power-up, does not access the keyboard LEDs until receiving a command from the host computer. When the keyboard controller performs a Basic Assurance Test (BAT) on power-up before receiving a host command, the controller does not turn on the LEDs. Upon receiving a Reset command from the host, the controller: (1) turns on the LEDs and performs a BAT with LEDs on; and (2) flashes the LEDs a second time to be compatible with the IBM PCs. Another feature of the invention is a non-destructive test of the controller RAM during BATs. The RAM is tested non-destructively both for the "stuck-at-1" and the "stuck-at-0" conditions. Still another feature is that the controller determines the state of the keyboard LEDs without reading a hardware port. The controller keeps track of the LED state by flags in the controller memory, and the controller determines the LED state by reading the flags.
