CS5535 datasheet(110/555 Pages) NSC

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Revision 0.8

4.9

KEYBOARD EMULATION LOGIC

The Keyboard Emulation Logic (KEL) provides a virtual

8042 keyboard controller interface that is used to map non-

legacy keyboard and mouse sources to this traditional

interface. For example, Universal Serial Bus (USB) sources

are “connected” to this interface via System Management

Mode (SMM) software. It also allows mixed environments

with one LPC legacy device and multiple new (USB)

devices. It produces IRQ and ASMI outputs.

Features

• Provides a virtual 8042 keyboard controller interface.

• Allows mixed environments.

• Produces IRQ and ASMI outputs.

• Employs a clock control logic for power management

purposes.

• No USB controller required for KEL to operate.

4.9.1

Keyboard Emulation and Port A

The Keyboard Emulation Logic (KEL) with Port A is illus-

trated in Figure 4-21. Strictly speaking, these are separate

functions. However, since they both effect the FA20#

(Force processor Address bit 20 to zero when low), the two

functions are implemented together. The Keyboard Emula-

tion Logic is the most complex and is discussed first.

Figure 4-21. KEL Block Diagram

Port A Write

& Read

KEL X

Control

USB1_SOF

Local Bus Clock

Reset

OUT

Local Bus Data

* Read-Back Multiplexer is not shown

USB2_SOF

1 kHz Clock

Keyboard

Emulator

Logic (KEL)

LPC_IRQ1

LPC_IRQ12

ASMI

EmulationEnable

SnoopEnable

FA20#

INIT Keyboard

IRQ 1 (to PIC Subsystem)

IRQ 12 (to PIC Subsystem)

EmulationInterrupt

Port A Enable

A20 Keyboard

INIT Port A

A20 Port A

Port 060h and

Port 064h Write

Port 060h

Read

Port 064h

Read

HCE

Control

HCE

Input

HCE

Output

HCE

Status

14 MHz

1 kHz

14 MHz

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