Hot plug control apparatus and method

1. A method for controlling the transmission of electrical signals through a pin on a hot plug bus that uses a bus controller, the bus connecting a computer node to a slot capable of accepting a hot plug device, output electrical signals being transmitted from an output port of the computer node to the pin using an output driver, input electrical signals being transmitted from the pin to an input port of the computer node, the method comprising:

in response to determining that the slot should be powered down, simultaneously (a) disabling the transmission of input electrical signals from the pin to the input port and (b) redirecting output electrical signals to the input port to form a loopback between the output port and the input port; and

causing the output driver to have a high output impedance, so that the pin is electrically isolated from the computer node.

2. The method of claim 1 , wherein determining includes receiving, in the bus controller, a signal having data that indicates that an individual has directed, using a graphical user interface, that the slot should be powered down.

3. The method of claim 1 , wherein the bus includes a multiplexer, the output of the multiplexer being coupled to the input port, two inputs of the multiplexer being coupled to the pin and the output port respectively, further wherein simultaneously disabling and redirecting comprises changing the multiplexer input setting from the pin to the output port.

4. The method of claim 1 , wherein causing the output driver to have a high output impedance includes disabling the output driver.

5. The method of claim 1 , wherein the bus controller includes a pull-up resistor switchably coupled with the pin, the method further electrically isolating the pull-up resistor from the pin after causing the output driver to have a high output impedance.

6. The method of claim 1 , wherein the high impedance is greater than about one mega-ohm.

7. A method for controlling the transmission of electrical signals through a pin on a hot plug bus that uses a bus controller, the bus connecting a computer node to a slot capable of accepting a hot plug device, the computer node having an output port and an input port configured to form a loopback, the method comprising:

in response to determining that the slot should be powered up, causing an output driver to have a low output impedance, so that the output port is electrically connected through the output driver to the pin; and

simultaneously (a) breaking the loopback between the output port and the input port and (b) enabling the transmission of electrical signals from the pin to the input port.

8. The method of claim 7 , wherein determining includes receiving, in the bus controller, a signal having data that indicates that an individual has directed, using a graphical user interface, that the slot should be powered up.

9. The method of claim 7 , wherein the bus includes a multiplexer, the output of the multiplexer being coupled to the input port, two inputs of the multiplexer being coupled to the pin and the output port respectively, and wherein simultaneously breaking and enabling comprises changing the multiplexer input setting from the output port to the pin.

10. The method of claim 7 , wherein causing the output driver to have a low output impedance includes enabling the output driver.

11. The method of claim 7 , wherein the bus controller includes a pull-up resistor switchably coupled with the pin, the method further comprising electrically connecting the pull-up resistor to the pin before causing the output driver to have a low output impedance.

12. The method of claim 7 , wherein the high impedance is greater than about one mega-ohm.

13. Apparatus for controlling the transmission of electrical signals through a pin on a hot plug bus, the bus connecting a computer node to a slot capable of accepting a hot plug device, the computer node having an output port and an input port, the apparatus comprising:

an output driver for transmitting output electrical signals from the output port to the pin;

an input memory for temporarily storing input electrical signals for transmission to the input port;

a multiplexer for selecting, for storing in the input memory, either input electrical signals from the pin or output electrical signals, the output of the multiplexer being coupled to the input memory, two inputs of the multiplexer being coupled to the pin and the output port respectively; and

float logic, responsive to float signals received from the computer node, to control the output driver and to control the multiplexer selection.

14. The apparatus of claim 13 , wherein the float logic is configured to respond to a command to power down the slot by:

controlling the selecting means to select output electrical signals for storing in the input memory; and

controlling the output driver to have a high output impedance.

15. The apparatus of claim 14 , further comprising a graphical user interface configured to generate the command to power down the slot.

16. The apparatus of claim 13 , wherein the float logic is configured to respond to a command to power up the slot by:

controlling the selecting means to select input electrical signals from the pin for storing in the input memory; and

controlling the output driver to have a low output impedance.

17. The apparatus of claim 16 , further comprising a graphical user interface configured to generate the command to power up the slot.

18. The apparatus of claim 13 , further including bridge core logic for implementing a bus protocol, the bridge core logic producing the set of float signals.

19. The apparatus of claim 13 , wherein the output driver has a transmitting impedance when transmitting signals to the bus and a float impedance when floating, the float impedance being greater than the transmitting impedance.

20. The apparatus of claim 13 , wherein the high impedance is greater than about one mega-ohm.