Legacy-Free Keyboard/Embedded Controller with SPI and LPC Docking Interface
7. The ring oscillator will be automatically turned off
8. The 8051 goes into Sleep mode.
In sleep mode, the UART is powered off if VCC2 is removed, but the RTC and 8051 are in powerdown
(sleep) mode. In Sleep mode, the LPC47N350 consumes less than 20µA, and all wake-up pins are still
active.
When the 8051 is in sleep mode, all of the clocks are stopped and the 8051 is waiting for an unmasked
wake-up event. When the wake-up event occurs, the ring oscillator is started and the 8051 starts
executing from where it stopped in the sleep Mode Sequence. Once running, the 8051 can access all
of the registers that are on VCC1 and if VCC2 is at 3.3V, it can access all of the registers on VCC2.
The 8051 that was running off the ring oscillator (internal) clock source switches to an external clock
source, and then turns off the ring oscillator (internal) clock source.
S yste m fully pow ere d
up an d runn ing .
R E S E T _O U T = low , 8 051 S TP _ C LK = 0.
80 51 ow n s F lash interface,
ru nnin g keybo ard code.
T he host eithe r issu es a us er-
de fine d com m an d to p ut the
80 51into slee p m ode, or
th e 8 051 co de determ ines
th at the 80 51 sho uld enter
sle ep m ode .
80 51 sw itch es its clock source
to th e ring oscilla tor.
80 51 m asks a ll interrup ts
exce pt for T 5IN T .
T he 805 1 m ay/m ay not tu rn
off V C C 2 to rest of system .
S LE E P F LA G = 1
P C O N .0 = 1
R ing oscillato r first gated off
from 80 51, th en turned off.
80 51 now in
slee p m ode,
80 51 clock stop ped .
Figure 12.3 Entering Sleep Mode
SMSC LPC47N350
139
Revision 1.1 (01-14-03)
DATASHEET
SMSC [ SMSC CORPORATION ]
