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HT6542B Datasheet(PDF) 5 Page - Holtek Semiconductor Inc |
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HT6542B Datasheet(HTML) 5 Page - Holtek Semiconductor Inc |
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5 / 7 page  Functional Description Power on When power is switched on, the HT6542B auto- detect the motherboard type(AT or PS/2), then disable the keyboard/mouse and waits for the self-test command to perform a self-test. If no error is detected during self-test, HEX 55 is registered in the output buffer (note that any value other than HEX 55 would indicate HT6542B failure) and the keyboard interface is enabled. The HT6542B is now ready to receive a system command or keyboard data. Keyboard/mouse data transmission The keyboard/mouse transmits data to the con- troller in an 11-bit format in sync, with the keyboard/mouse clock signal. If this transmis- sion is not completed within the specified pe- riod, the HT6542B will register HEX FF into the output buffer and set the "transmit time- out" error bit in the STATUS REGISTER to 1. Controller data transmission The controller transmits data to the key- board/mouse in the same manner as it receives data from the keyboard/mouse. When the HT6542B starts transmitting data and the key- board/mouse does not start receiving (does not start clocking) or data transmission is not com- pleted within 15ms, the HT6542B will register HEX FE into the output buffer and set the "transmit time-out" error bit in the STATUS REGISTER to 1. Keyboard inhibited (KBD-INH to low) If the KBD-INH is switched to low, the key- board/mouse is inhibited. The HT6542B receive keyboard/mouse code and check the KBD-INH status, if inhibited the keyboard SCAN CODE and mouse code will be ignored and the key- board/mouse command response is registered into the HT6542B’s output buffer. Status register notations The STATUS REGISTER is located in HEX 64 of the I/O. It provides the HT6542B and inter- face status to the system. The following are the definitions for each bit: • b0(OBF): Output buffer full This bit is set while the HT6542B is sending data to the output buffer and cleared when the system reads the output buffer(I/O HEX 60H). • b1(IBF): Input buffer full This bit is set while the system is sending data to the HT6542B’s input buffer and cleared when the HT6542B reads the input buffer data. • b2: System flag This bit is 0 after power-on reset, set to 1 after self-test OK. • b3: Command/Data When the system writes the data to the HT6542B from I/O 64H, this bit becomes 1. Reset to 0 if from I/O 60H. • b4: This bit reflects the KBD-INH status when- ever data is placed in the HT6542B’s output buffer. • b5: Auxiliary Output Buffer Full. 0: The HT6542B’s output buffer is a keyboard data. 1: The HT6542B’s output buffer is a mouse data. • b6: Transmit time-out Set to 1 when the keyboard or mouse is not able to completely transmite data to the HT6542B within the specified period. • b7: Parity error 1: The HT6542B has received the key- board/mouse code with a parity error. (should be odd parity). Output buffer The output buffer is located in I/O HEX 60. It is used to transmit keyboard/mouse code or key- board controller response data. The output buff- er data is valid only when OBF=1. Input buffer The input buffer is located in I/O HEX 60 or HEX 64. The system writes command and data into this port in the following categories: • Data written to I/O HEX 64 as command write. • Data written to I/O HEX 60 as data write. HT6542B 5 30th Nov ’95 |
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