Bi-directional buffer with level shifting

A method for bi-directional buffering using first voltage buffer circuitry that causes a first node to follow a second node, and second voltage buffer circuitry that causes the second node to follow the first node, the method comprising:

• (a) enabling the first voltage buffer circuitry and the second voltage buffer circuitry when
• a voltage of the first node does not exceed a first threshold voltage, and/or
• a voltage of the second node does not exceed a second threshold voltage;
• and
• (b) disabling the first voltage buffer circuitry and the second voltage buffer circuitry when
• the voltage of the first node exceeds the first threshold voltage, and
• the voltage of the second node exceeds the second threshold voltage.

A bi-directional buffer, comprising:

• first voltage buffer circuitry that causes a first node to follow a second node;
• second voltage buffer circuitry that causes the second node to follow the first node;
• and
• further circuitry to selectively enable or disable the first voltage buffer circuitry and the second voltage buffer circuitry;
• wherein the further circuitry enables the first voltage buffer circuitry and the second voltage buffer circuitry when a voltage of the first node does not exceed a first threshold voltage, and/or a voltage of the second node does not exceed a second threshold voltage;
• and
• wherein the further circuitry disables the first voltage buffer circuitry and the second voltage buffer circuitry when the voltage of the first node exceeds the first threshold voltage, and the voltage of the second node exceeds the second threshold voltage.

A system comprising:

• a first bus line segment;
• a second bus line segment;
• a first pull-up resistor connected between the first bus line segment and a first high voltage supply rail;
• and
• a second pull-up resistor connected between the second bus line segment and a second high voltage supply rail;
• a bi-directional buffer, connected between the first and second bus line segments;
• and
• circuitry to selectively enable and disable the bi-directional buffer;
• wherein the circuitry enables the bi-directional buffer when a voltage of the first bus line segment does not exceed a first threshold voltage, and/or a voltage of the second bus line segment does not exceed a second threshold voltage;
• wherein the circuitry disables the bi-directional buffer when the voltage of the first bus line segment exceeds the first threshold voltage, and the voltage of the second bus line segment exceeds the second threshold voltage;
• and
• wherein when the bi-directional buffer is disabled, the first bus line segment can be pulled up to the first voltage supply rail, and the second bus line segment can be pulled up to the second voltage supply rail.

A printed circuit board (PCB) card, comprising:

• a terminal that connects the PCB card to a system backplane;
• a bi-directional buffer, connected between the terminal and an internal node of the PCB card;
• and
• circuitry to selectively enable and disable the bi-directional buffer;
• wherein the circuitry enables the bi-directional buffer when a voltage of the terminal does not exceed a first threshold voltage, and/or a voltage of the internal node does not exceed a second threshold voltage;
• and
• wherein the circuitry disables the bi-directional buffer when the voltage of the terminal exceeds the first threshold voltage, and the voltage of the internal node exceeds the second threshold voltage.

A method for providing bi-directional buffering between a first node and a second node, wherein the first node is connected by a first pull-up resistor to a first voltage supply rail, and the second node is connected by a second pull-up resistor to a second voltage supply rail that is different than the first voltage supply rail, the method comprising:

• (a) allowing a voltage of the first node to follow a voltage of the second node, and the voltage of the second node to follow the voltage of the first node, when
• the voltage of the first node does not exceed a first threshold voltage, and/or
• the voltage of the second node does not exceed a second threshold voltage;
• and
• (b) allowing the voltage of the first node to be pulled up to the voltage of the first voltage supply rail, and the voltage of the second node to pulled up to the voltage of the second voltage supply rail, when
• the voltage of the first node exceeds the first threshold voltage, and
• the voltage of the second node exceeds the second threshold voltage.