MEC1404 Datasheet, PDF (403/572 Pages) Microchip Technology – Keyboard and Embedded Controller Products for Notebook PC

MEC140X/1X
29.12 PS/2 Port Physical Layer Byte Transmission Protocol
The PS/2 physical layer transfers a byte of data via an eleven bit serial stream as shown in TABLE 29-2:. A logic 1 is
sent at an active high level. Data sent from a Keyboard or mouse device to the host is read on the falling edge of the
clock signal. The Keyboard or mouse device always generates the clock signal. The Host may inhibit communication
by pulling the Clock line low. The Clock line must be continuously high for at least 50 microseconds before the Keyboard
or mouse device can begin to transmit its data. See Table 29-3, "PS/2 Port Physical Layer Bus States".
TABLE 29-2: PS/2 PORT PHYSICAL LAYER BYTE TRANSMISSION PROTOCOL
Bit
Function
1
Start bit (always 0)
2
Data bit 0 (least significant bit)
3
Data bit 1
4
Data bit 2
5
Data bit 3
6
Data bit 4
7
Data bit 5
8
Data bit 6
9
Data bit 7 (most significant bit)
10
Parity bit (odd parity)
11
Stop Bit (always 1)
FIGURE 29-3:
PS/2 PORT PHYSICAL LAYER BYTE TRANSMISSION PROTOCOL
PS2CLK ^{CLK 1}
CLK2
CLK3
CLK9
CLK10
CLK11
PS2DATA ^{Start Bit}
Bit 0
Bit 1
Bit 7
Parity
Stop Bit
TABLE 29-3: PS/2 PORT PHYSICAL LAYER BUS STATES
Data
high
high
low
Clock
high
low
low
State
Idle
Communication Inhibited
Request to Send
29.13 Controlling PS/2 Transactions
PS/2 transfers are controlled by fields in the PS2 Control Register.
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