Input/output circuit for handling unconnected I/O pads
View Patent ↗A circuit coupled to an input-output bond pad (I/O pad) in an integrated circuit including an input buffer, an output buffer and a pad management circuit. The pad management circuit receives a first data signal, a first output enable signal, and a configuration signal indicative of the connection state of the I/O pad, and generates a second data signal and a second output enable signal. When the configuration signal indicates the I/O pad is to be connected to a package pin, the pad management circuit couples the first data signal as the second data signal and couples the first output enable signal as the second output enable signal. When the configuration signal indicates the I/O pad is to be left unconnected, the pad management circuit asserts the second output enable signal and generates the second data signal having a predetermined value.
1. A circuit coupled to an input-output bond pad (I/O pad) in an integrated circuit, the circuit comprising:
an input buffer having an input terminal coupled to the I/O pad, an output terminal providing an input data value for the integrated circuit;
an output buffer having a data input terminal coupled to receive a first data signal, an output enable terminal coupled to receive a first output enable signal, and an output terminal coupled to the I/O pad, the output buffer driving the I/O pad to a voltage level corresponding to the first data signal when the first output enable signal is asserted;
a pad management circuit having a first input terminal receiving a second data signal, a second input terminal receiving a second output enable signal, and a third input terminal receiving a configuration signal indicative of the connection state of the I/O pad, the pad management circuit generating the first data signal and the first output enable signal,
wherein the configuration signal has a first value indicating a normal mode where the I/O pad is to be connected to a package pin in an integrated circuit package and the configuration signal has a second value indicating an unconnected mode where the I/O pad is to be left unconnected in the integrated circuit package; and
wherein when the configuration signal has the first value, the pad management circuit couples the second data signal as the first data signal and couples the second output enable signal as the first output enable signal; and when the configuration signal has the second value, the pad management circuit asserts the first output enable signal and generates the first data signal having a predetermined value.
2. The circuit of claim 1 , wherein in the unconnected mode, the pad management circuit generates the first data signal having a predetermined value that is compatible with the operation of the integrated circuit.
3. The circuit of claim 2 , wherein the predetermined value of the first data signal comprises a fixed data value.
4. The circuit of claim 2 , wherein the predetermined value of the first data signal comprises a data value that varies according to the operation of the integrated circuit.
5. The circuit of claim 1 , wherein the predetermined value of the first data signal is driven to the output terminal of the input buffer through the I/O pad.
6. The circuit of claim 1 , further comprising:
a memory device storing the configuration information of the integrated circuit and providing the configuration information to the pad management circuit.
7. The circuit of claim 6 , wherein the memory device comprises one of a RAM, a PROM, an EEPROM, fuses and anti-fuses.
8. The circuit of claim 6 , wherein the memory device comprises a memory element coupled to a second I/O pad for receiving the configuration information from the second I/O pad.