CS5535 Datasheet, PDF (110/555 Pages) National Semiconductor (TI) – Geode™ CS5535 I/O Companion Multi-Function South Bridge

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.
14 MHz
14 MHz
to
1 kHz
Reset
Local Bus Clock
USB1_SOF
USB2_SOF
1 kHz Clock
LPC_IRQ1
LPC_IRQ12
KEL X
Control
IRQ 1 (to PIC Subsystem)
IRQ 12 (to PIC Subsystem)
EmulationInterrupt
ASMI
EmulationEnable
SnoopEnable
FA20#
INIT Keyboard
A20 Keyboard
INIT Port A
A20 Port A
Port A Enable
Keyboard
Emulator
Port A Write
& Read
*
HCE
Control
Logic (KEL)
*
HCE
Input
*
HCE
Output
*
HCE
Status
Port 060h and
Port 064h Write
*
Port 060h
Read
*
Port 064h
Read
32 32
8
8
IN OUT
Local Bus Data
* Read-Back Multiplexer is not shown
OUT IN
Local Bus Data
Figure 4-21. KEL Block Diagram
www.national.com
110
Revision 0.8