
Section 16 LPC Interface (LPC)
Rev. 1.00 Mar. 02, 2006 Page 562 of 798
REJ09B0255-0100
There are two modes
continuous mode and quiet modefor serialized interrupts. The mode
initiated in the next transfer cycle is selected by the stop frame of the serialized interrupt transfer
cycle that ended before that cycle.
In continuous mode, the host initiates host interrupt transfer cycles at regular intervals. In quiet
mode, the slave with interrupt sources requiring a request can also initiate an interrupt transfer
cycle, in addition to the host. In quiet mode, since the host does not necessarily initiate interrupt
transfer cycles, it is possible to suspend the clock (LCLK) supply and enter the power-down state.
In order for a slave to transfer an interrupt request in this case, a request to restart the clock must
first be issued to the host. For details see section 16.4.6, LPC Interface Clock Start Request.
16.4.6
LPC Interface Clock Start Request
A request to restart the clock (LCLK) can be sent to the host by means of the
CLKRUN pin. With
LPC data transfer and SERIRQ in continuous mode, a clock restart is never requested since the
transfer cycles are initiated by the host. With SERIRQ in quiet mode, when a host interrupt
request is generated the
CLKRUN signal is driven and a clock (LCLK) restart request is sent to
the host. The timing for this operation is shown in figure 16.7.
CLK
CLKRUN
Pull-up enable
Driven by the host processor
Driven by the slave processor
1
2
3
4
5
6
Figure 16.7 Clock Start Request Timing
Cases other than SERIRQ in quiet mode when clock restart is required must be handled with a
different protocol, using the
PME signal, etc.