Legacy-Free Keyboard/Embedded Controller with SPI and LPC Docking Interface
System is running
(Vcc2 and Vcc1 are on)
8051 is executing
Host resets the
8051STP_CLK[0] bit
Stop Clock
Counter
= 0
No
Keyboard firmware
Yes
Reset Event is conveyed
to the 8051 via a command
from host or GPIO
nRESET_OUT deasserted
No
8051 IRQ
Yes
nRESET_OUT deasserted
and 8051 STP_CLK[0] = 1
stops the 8051 clock.
iRESET_OUT register
bit is reset causing
nRESET_OUT pin to be
asserted (See note 1)
Host may program the
Flash memory via the
LPCBUS Flash Program
Access Mode
8051 wakes up from Idle
Mode and starts executing
from where it left off
8051 goes into Idle Mode
Note 1:
Note 2: In order to leave Idle Mode, the 8051
must receive an interrupt; typically a software
timer interrupt will be used.
Clearing the iRESET_OUT bit causes the following:
.
8051 STP_CLK[0] = 1
Stop Clock Counter starts decrementing
.
Figure 7.2 Typical System Reset Sequence
7.4
CPU RESET Sequence
Often the Host CPU (Pentium) is reset by the hardware signal, CPU_RESET, which is issued by
software to switch the Processor from Protected, or “Virtual 86”, mode back to Real mode.
CPU_RESET can be generated from the LPC47N350 8051 core or it may be generated from other logic
on the PC motherboard. CPU_RESET is meant only to reset the CPU; the rest of the system continues
to run normally, including the keyboard BIOS in the 8051.
7.5
8051 Clock Controls
The LPC47N350 has two clock source:
The 8051 may program itself to run off of an internal ring oscillator having a frequency range between
4 and 12MHz. This is not a precise clock, but is meant to provide the 8051 with a clock source when
VCC2 is shut down in the system.
When VCC2 is powered, the 8051 may be programmed to run off the PLL. The 14.318MHz external
clock source. The 8051 PLL clock frequenies are programmable.
7.5.1
Frequency Controls
The KBDCLK ENABLE bit controls the running of the 8051 PLL clock and the KBDCLK[1:0] control bits
in the KSTP_CLK register (MMCR 0x7F27) select the 8051 system clock frequencies. The LPC47N350
8051 can run up to 32MHz.
Revision 1.1 (01-14-03)
SMSC LPC47N350
DATA4S4HEET
SMSC [ SMSC CORPORATION ]
