EC Required Knowledge - KBC

EC Required Knowledge

The first step for a software engineer is to thoroughly understand the relevant specifications, just as understanding the requirements is essential before developing software. Similarly, an EC engineer needs to have a clear understanding of LPC, SMBUS, PS2, KBC, and other related knowledge before moving on to the next step.

Keyboard Controller

The earliest keyboard controller was the Intel 8042, which mainly consisted of four registers and three I/O control ports. The four registers were a BYTE input buffer register, a BYTE output buffer register, a status register, and a control register.

The definitions of the three I/O control ports are shown in the table below:

• PORT #1

Port 1 [ Input Port ]
Pin	Name	Function
0	P10	Keyboard Data [PS/2]
1	P11	Mouse Data [PS/2]
2	P12
3	P13
4	P14	External ROM 1:Enable  0:Disable
5	P15	Manufacturing Setting 1:Enable 0:Disable
6	P16	Display Type Switch 1:Color 0:Monochrome
7	P17	Keyboard Inhibit Switch 1:Enable 0:Disable

• PORT #2

Port 2 [ Output Port ]
Pin	Name	Function
0	P20	System Reset 1:Nornal 0:Reset
1	P21	Gate A20
2	P22	Mouse Data [PS/2] 1:Pull Data low 0:High –Z
3	P23	Mouse Clock [PS/2] 1:Pull Data low 0:High –Z
4	P24	Input Buffer Full / Keyboard IBF interrupt [PS/2] 1:Assert IRQ 1 0:Deassert IRQ1
5	P25	Output Buffer Empty / Mouse IBF interrupt [PS/2] 1:Assert IRQ 12 0:De-assert IRQ12
6	P26	Keyboard Clock 1:Pull Clock low 0:High Z
7	P27	Keyboard Data 1:Pull Data low 0:High Z

• PORT #3

Port 3 [ Test Port ]
Pin	Name	Function
0	T0	Keyboard Clock
1	T1	Keyboard Data
2
3
4
5
6
7

• Status Register

	7	6	5	4	3	2	1	0
AT – Compatible Mode	PERR	RxTO	TxTO	INH	A2	SYS	IBF	OBF
PS/2 – Compatible Mode	PERR	TO	MOBF	INH	A2	SYS	IBF	OBF

• OBF(Output Buffer Full) – Indicates that data has been written to the 8042's output buffer.

• IBF(Input Buffer Full) – The system writes data to the 8042 input buffer.

• SYS(System Flag) – Indicates whether the system is Warning Boot or Cold Boot. "1" indicates Warning Boot.

• A2(Address line 2) – Indicates whether system data is written to I/O PORT 0x64 or 0x60. "1" indicates PORT 0x64.

• INH(Inhibit flag) – Indicates whether the system and PS/2 KEYBOARD interface are functioning correctly. LOW indicates that the clock is set to LOW, meaning that communication between the system and PS/2 KEYBOARD is disabled.

• TxTO(Transmit Timeout) – The system sends a command to the keyboard but it is not received within the time limit, meaning there may be no keyboard on the system. "0" indicates that no timeout occurred.

• RxTO(Receive Timeout) – Indicates that the keyboard did not respond to the system command within the time limit. "0" indicates that no timeout occurred.

• PERR(Parity Error) – Indicates that there is incorrect data being transmitted between the system and the keyboard. "0" indicates that there is no incorrect data.

• MOBF(Mouse Output Buffer Full) – Indicates that data has been sent to the output buffer of the PS/2 mouse.

• TO(General Timeout) – Indicates that the command was not received within the time limit or that the KEYBOARD did not respond to the system command within the time limit.

• Control Register

	7	6	5	4	3	2	1	0
AT – Compatible Mode		XLAT	PC	_IN	OVR	SYS		INT
PS/2 – Compatible Mode		XLAT	_EN2	_IN		SYS	INT2	INT

• INT(Output Buffer Full Interrupt) – Controls whether to send IRQ 1 to the system when there is data in the keyboard output buffer.

• SYS(System Flag) – Indicates a system boot event. "1" indicates Warning Boot.

• OVR(Inhibit Override) – Controls whether the interface between the KBC and the system is disabled via the I/O PIN.

• _IN(Disable Keyboard) – Setting this bit will stop the keyboard from sending data to the system.

• PC (PC Mode) –

• XLAT(Translate Scan Code) – Sets the keyboard Scan Code Set; "1" indicates Code Set 1.

• _INT2(Mouse Output Buffer Full Interrupt) – Controls whether to send IRQ 12 to the system when there is data in the mouse output buffer.

• _EN2(Disable Mouse) - Setting this bit will stop the mouse from sending data to the system.

• How does the system read and write KBC?

• Before writing instructions to the KBC, the system must first check if there are any instructions or data that have not yet been retrieved from the KBC's input buffer. Then, it sends the instructions or data to the KBC.

WaitIBE:           in      al,64h           and     al,10b jnz WaitIBE           out     60h,cl

• Before reading data from the KBC, the system must first check whether there is any data written by the KBC in the KBC's output buffer, and then read the data.

WaitOBF:           in      al,64h           and     al,01b           jz      WaitOBF           in      al,60h

• Keyboard Controller Command

System commands are transmitted to the KBC via PORT 0x64, and system data is transmitted to the KBC via PORT 0x60. The KBC then performs the relevant actions on the commands and data. The KBC commands are as follows:

• 0x20 (Read Command Byte) – Reads the control bits of the KBC.

• 0x60 (Write Command Byte) – Control bits written to the KBC

• 0x90-0x9F (Write to output buffer) –

• 0xA1 (Get firmware version) – Get the KBC firmware version

• 0xA4 (Get password) – Check if a password has been set. If a password has been set, KBC will respond with 0xFA; if no password has been set, KBC will respond with 0xF1.

• 0xA5 (Set password) – Sets the user password.

• 0xA6 (Check password) – Compares the entered password to ensure it is correct.

• 0xA7 (Disable mouse interface)

• 0xA8 (Enable mouse interface)

• 0xA9 (Mouse interface test) – Test the mouse interface.

Value	Description	Value	Description
0x0	OK	0x3	Data Line 為 LOW
0x1	Clock line is LOW	0x4	Data Line 為 HIGH
0x2	Clock line is HIGH

• 0xAA (Controller self test) – KBC self-test. A successful self-test will respond with 0x55 to the system.

• 0xAB (Keyboard interface test) – Test the keyboard interface.

Value	Description	Value	Description
0x0	OK	0x3	Data Line 為 LOW
0x1	Clock line is LOW	0x4	Data Line 為 HIGH
0x2	Clock line is HIGH

• 0xAD (Disable Keyboard interface)

• 0xAE (Enable Keyboard interface)

• 0xAF (Get version)

• 0xC0 (Read Input port) – Read input port [PORT 1]

• 0xC1 (Copy input port low nibble) - Reads bits [0:3] of input port [PORT 1] and copies them to the status register.

• 0xC2 (Copy input port high nibble) – Reads bits [4:7] of input port [PORT 1] and copies them to the status register.

• 0xD0 (Read output port) – Read output port [PORT 2]

• 0xD1 (Write output port) – Writes data to output port [PORT 2]

• 0xD2 (Write Keyboard buffer) – Writes data to the keyboard output buffer.

• 0xD3 (Write Mouse buffer) – Writes data to the mouse's output buffer.

• 0xD4 (Write Mouse Device) – Writes data or commands to the mouse.

• 0xE0 (Read Test Port) – Read test port [PORT 3]

• 0xFE (Warning Start) – Initiate CPU Reset