Background of the Invention

(1) Field of the Invention:

The present invention relates to electrical equipment; more specifically, interfacing to a bus interface without removing power lrom that electrical interface.

(2) Description of the Related Art:

In many applications using electrical equipment, it is desirable to provide an uninterrupted service. For example, a computer acting as a server for a local area network should be very reliable because any downtime on the server interferes with many users. In an effort to reduce downtime, electrical equipment typically includes a large amount of redundancy, i.e., several circuit cards performing the same function. This enables die computer or electrical equipment to use one of the redundant electrical cards if a failure occurs in a card presently being used. This permits the equipment to continue operating without producing "downtime". The failed circuit cards should be replaced so as to maintain a high level of redundancy if there are any other additional failures. In the past, replacing circuit cards in equipment not specifically designed for "Hot" insertion, involved powering down or turning off the equipment in which the card is located. This results in an interruption of service to users dependent on the piece of equipment As a result, it is desirable to replace circuit cards without turning power off to the equipment in which the card is located. When replacing a circuit card without turning power off, there is a danger of applying signals to an unpowered device or introducing unwanted transient conditions onto a communication bus and thereby interfering widi die operation of die electrical equipment or possibly causing a failure.

Summary of the Invention

A circuit card is interfaced to a powered electrical bus by applying power to the circuit card before it interfaces to die electrical bus or by removing power from die circuit card after it has been removed from the bus. This is accomplished using a power cord mat connects die equipment's power supply to a mating edge connector on die card to be inserted or removed. Attaching die power cord to the mating edge connector of die card disables die output drivers that provide output signals to die equipment's communication bus. This prevents introducing error signals onto die communication bus. Additionally, the contacts on die edge

connector are sequenced to prevent applying power to die circuit card before a ground is available. Additionally, the power cord and circuit card are keyed to prevent improper insertion, and an inductor is included in die power cardrto prevent surge currents.

Brief Description of the Drawings

FIG. 1 illustrates die insertion/removal of a circuit card using a power cord;

FIG. 2 illustrates die circuit card of FIG. 1 and its keyed edge connectors; and FIG. 3 illustrates die upper edge connector of die circuit card of FIG. 2.

Detailed Description of the Invention

FIG. 1 illustrates die insertion/removal of circuit card 10 from personal computer 12. Personal computer 12 includes power supply 14. Signals including power, data and control signals are distributed diroughout computer 12 by an electrical bus such as an ISA bus. Other types of standard and nonstandard buses may be used. Edge connector 16 of circuit card, 8 and 10 interface widi one of connectors 17 which are in electrical contact widi the computer's electrical bus. Typically, in a computer system, power supply 14 includes a unused power connector such as power connector 18. Power connector 18 is connected to power cord 20. Power cord 20 includes connector 22 which mates widi connector 18 of power supply 14. At die other end of power cord 20 is connector 24 which mates widi edge connector 26 of circuit card 10. It should be noted that other types of mating connectors widi sequenced power and ground contacts may be used in place of connectors 24 and 26. Power cord 20 should also include surge filter 28. Surge filter 28 may be a commercially-available surge filter or a simple inductor.

When circuit card 10 is to be inserted into personal computer 12 widiout turning off power supply 14, power cord 20 is used. Initially, connector 22 of power cord 20 is mated widi connector 18 of power supply 14. Next, connector 24 of power cord 20 is mated widi edge connector 26 of circuit card 10. Edge connector 26 and connector 24 are keyed so that they only mate in one way and dierefore cannot be accidentally reversed. When connector 24 is mated widi connector 26, die contacts on edge connector 26 are sequenced so mat ground contact is made before power contact is made. Additionally, connector 24 shorts togetiier some contacts on edge connector 26 so tiiat the circuitry on circuit card 10 is put in a benign state. Alternatively, connector 24 may apply ground or power to one or more contacts of

connector 26 to place the circuit card in a benign state. For example, a benign state is a state where driver circuitry that electrically interfaces to computer 12's bus through edge connector 16 is disabled and die circuitry on circuit card 10 is put in a reset, known or predetermined state so mat incorrect signals are not put on to the bus when die drivers are enabled.

After connectors 24 and 26 are mated, circuit card 10 is inserted into computer 12 so that edge connector 16 mates with connector 17 of computer 12's electrical bus. As was widi edge connector 26, edge connector 16 is keyed to prevent improper mating between edge connector 16 and connector 17. After edge connector 16 is mated widi die connector of die electrical bus, power cord 20 is disconnected by disconnecting connectors 24 and 26, and optionally disconnecting connectors 22 and 18. Circuit card 10 has now been mated with computer 12's bus without powering down power supply 14 while preventing incorrect signaling on die bus. Circuit card 10 can be removed from computer 12 without powering down power supply 14 by first connecting connector 22 to connector 18 and then connector 24 to connector 26. After power cord 20 has been installed, circuit card 10 may be removed by disengaging connector 16 from connector 17. After connector 16 has been disengaged, connectors 24 and 26 may be disengaged to remove die card.

FIG. 2 illustrates circuit card 10. Circuit card 10 includes edge connector 16 and edge connector 26. It also includes electrical components such as electrical components 30. Edge connector 26 has keyway 32 which mates widi a corresponding key of connector 24. Electrical contacts 38 of edge connector 26 mate with electrical contacts witiiin connector 24. Similarly, edge connector 16 has keyway 40 which mates widi a corresponding key of connector 17. Connector 17 is electrically connected to computer 12's bus. Electrical contacts 42 of connection 16 mate widi electrical contacts within connector 17.

FIG. 3 is an enlargement of edge connector 26. Keyway 32 is visible. It should be noted that contacts 38 are sequenced. For example, contacts 50, 52, 54, 56 and 64 are connected to ground conductor of circuit card 10 and contacts 58, 60, and 62 are connected to die power conductors of circuit card 10. Since die ground connection contacts are closer to die edge of edge connector 26, they will make contact widi titeir corresponding contacts of connector 24 before contact is made between power contacts 58, 60 and 62, and their corresponding contacts of connector 24. This provides a sequenced connection where ground contact is made before power contact is made. Additionally, reset contact 65 is shorted to ground 64 when

connector 24 is attached. This sets circuit board 10 into a benign or reset state so that when die board is eventually enabled onto computer 12's bus, die circuit board is enabled from a known state and thereby prevents sending incorrect signaling over the bus.