Keyboard, mouse interface circuit analysis and maintenance.

1. Keyboard, mouse interface introduction.

Keyboard, mouse interface for P/S2 interface, is an important input interface for the user control computer. The P/S2 interface on the motherboard is shown in figure 1, and the definition of the PS2 interface is shown in Table 1.

 Figure 1 P/S2 interface.                            Table 1 P/S2 interface definitions. 

2. P/S2 keyboard, mouse interface working principle.

The P/S2 interface works as shown in figure 2. On the Intel,AMD,nVIDIA chipset motherboard on the market, the P/S2 interface is controlled by the IO chip input / output manager. Interface 4-pin and 10-pin for keyboard, mouse provides 5V power supply, the DAT,CLK is a data line and a clock line, respectively, connected to the IO chip, and through the middle of the drag pull up to 5V power supply, and filter capacitance and inductance. IO chip power supply, After the clock signal is normal, the keyboard and mouse are initialized when the power is on, when the user presses the keyboard or mouse and passes through the data line, the clock line is transmitted to the IO chip for processing, and then the IO chip is sent to the South Bridge chip through the LPC bus. After the internal treatment of the south bridge, the corresponding operation is realized.

 Fig. 2 schematic diagram of P/S2 interface.

3. Maintenance method of P/S2 interface fault.

P/S2 interface failure will lead to keyboard, mouse can not be used, or unstable, sometimes can be used, sometimes can not be used, in DOS can be used normally, but not into the Windows system can not use, and so on. The maintenance method is as follows.

1) Check the P/S2 interface for reaming, pin breaking, swaps.

2)Measuring P/S2 interface VCC power supply 5V.

3) Interface data line and clock line to ground value, normal value is 500 kx700. Lower value, remove filter capacitor or replace IO chip; high value, check whether the wire jumper is broken or replace the IO chip.

4)If the P/S2 interface power supply, the data cable is normal, first replace pull-up and drain, the fault is still the case, finally replace IO chip.

This article is from Allicdata Electronics Limited. Reprinted need to indicate the source.