Security hardened function keys and indicators
A key-press detection circuit for an information handling system includes a detector circuit, a RC circuit, and a latch circuit. The detector circuit is coupled to a keyboard matrix device, and operates to provides a clock signal in a first state when a particular key of the keyboard matrix device is pressed and to provide the clock signal in a second state when the particular key is not pressed. The RC circuit receives the clock signal and provides a timed clock signal in a third state for a predetermined amount of time in response to receiving the clock signal in the first state. After the predetermined amount of time, the RC circuit provides the timed clock signal in a fourth state. The latch circuit receives the timed clock signal at a clock input, receives a data signal at a data input, and latches an output signal in a same state as the data signal when the timed clock signal changes from the third state to the fourth state.
1. A key-press detection circuit for an information handling system, the key-press detection circuit comprising:
a detector circuit coupled to a keyboard matrix device, the detector circuit configured to provide a clock signal in a first state when a particular key of the keyboard matrix device is pressed and to provide the clock signal in a second state when the particular key is not pressed;
a resistor-capacitor (RC) circuit configured to receive the clock signal and to provide a timed clock signal in a third state for a predetermined amount of time in response to receiving the clock signal in the first state, wherein after the predetermined amount of time, the RC circuit is further configured to provide the timed clock signal in a fourth state; and
a latch circuit configured to receive the timed clock signal at a clock input, to receive a data signal at a data input, and to latch an output signal in a same state as the data signal when the timed clock signal changes from the third state to the fourth state.
2. The key-press detection circuit of claim 1 , wherein the detector circuit comprises a NOR-gate having a first logic input, a second logic input, and a logic output.
3. The key-press detection circuit of claim 2 , wherein the first logic input is coupled to a selected one of a plurality of row enable signals to the keyboard matrix, the selected row enable signal being associated with the particular key.
4. The key-press detection circuit of claim 3 , wherein the second logic input is coupled to a selected one of a plurality of column enable signals from the keyboard matrix, the selected column enable signal being associated with the particular key.
5. The key-press detection circuit of claim 4 , wherein the first logic input and the logic second input are both in a low state only when the particular key is pressed.
6. The key-press detection circuit of claim 5 , wherein, when the first logic input and the logic second input are both in the low state, the logic output is in the first state.
7. The key-press detection circuit of claim 1 , wherein the output signal operates to control a function associated with the particular key.
8. The key-press detection circuit of claim 7 , wherein the output signal further operates to drive an indicator associated with the function.
9. The key-press detection circuit of claim 1 , wherein the particular key is associated with a microphone function of the information handling system.
10. The key-press detection circuit of claim 1 , wherein the particular key is associated with an electromagnetic camera shutter of the information handling system.
11. A method, comprising:
receiving, at a detector circuit coupled to a keyboard matrix device, an indication that a key of the keyboard matrix has been pressed;
determining that the key is a particular key;
providing a clock signal in a first state when the particular key is pressed;
providing the clock signal in a second state when the particular key is not pressed;
receiving, at a resistor-capacitor circuit, the clock signal;
providing a timed clock signal in a third state for a predetermined amount of time in response to receiving the clock signal in the first state;
providing, after the predetermined amount of time, the timed clock signal in a fourth state;
receiving, by a latch circuit, the timed clock signal at a clock input;
receiving, by the latch circuit, a data signal at a data input; and
latching an output signal in a same state as the data signal when the timed clock signal changes from the third state to the fourth state.
12. The method of claim 11 , wherein the detector circuit comprises a NOR-gate having a first logic input, a second logic input, and a logic output.
13. The method of claim 12 , further comprising coupling the first logic input to a selected one of a plurality of row enable signals to the keyboard matrix, the selected row enable signal being associated with the particular key.
14. The method of claim 13 , further comprising coupling the second logic input to a selected one of a plurality of column enable signals from the keyboard matrix, the selected column enable signal being associated with the particular key.
15. The method of claim 14 , wherein the first logic input and the logic second input are both in a low state only when the particular key is pressed.
16. The method of claim 15 , wherein, when the first logic input and the logic second input are both in the low state, the logic output is in the first state.
17. The method of claim 11 , further comprising controlling a function associated with the particular key based upon the output signal.
18. The method of claim 17 , further comprising driving an indicator associated with the function based upon the output signal.
19. The method of claim 11 , wherein the particular key is associated with one of a microphone function of the information handling system, and an electromagnetic camera shutter of the information handling system.
20. A keyboard circuit of an information handling system, the keyboard circuit comprising:
key-press detection circuit, including:
a detector circuit coupled to a keyboard matrix device, the detector circuit configured to provide a clock signal in a first state when a particular key of the keyboard matrix device is pressed and to provide the clock signal in a second state when the particular key is not pressed;
a resistor-capacitor (RC) circuit configured to receive the clock signal and to provide a timed clock signal in a third state for a predetermined amount of time in response to receiving the clock signal in the first state, wherein after the predetermined amount of time, the RC circuit is further configured to provide the timed clock signal in a fourth state; and
a latch circuit configured to receive the timed clock signal at a clock input, to receive a data signal at a data input, and to latch an output signal in a same state as the data signal when the timed clock signal changes from the third state to the fourth state;
a startup circuit configured to drive the timed clock signal to the third state when the information handling system is powered up; and
an embedded controller configured to retrieve a stored data value when the information handling system is powered up, and to provide the data value to the data input while the startup circuit drives the timed clock signal.