GXM datasheet(178/244 Pages) NSC

178 / 244 page

www.national.com

178

Revision 3.1

Power Management (Continued)

6.5.4

Stopping the Input Clock

Because the GXm processor is a static device, the input

clock (SYSCLK) can be stopped and restarted without

any loss of internal CPU data. If DRAMS are used that do

not have self-refresh, bit 0 of the PM Clock Stop Control

must be continuously applied to keep the refresh circuitry

running. The SYSCLK input can be stopped at either a

logic high or logic low state. The required sequence for

stopping SYSCLK is to initiate CPU Suspend mode, wait

for the assertion of SUSPA# by the processor, and then

stop the input clock.

The CPU remains suspended until SYSCLK is restarted

and the Suspend mode is exited as described earlier.

While SYSCLK is stopped, the processor can no longer

sample and respond to any input stimulus including

REQx#, NMI, SMI#, INTR, and RESET inputs.

Figure 6-4 illustrates the recommended sequence for

stopping the SYSCLK using SUSP# to initiate Suspend

mode. SYSCLK may be started prior to or following nega-

tion of the SUSP# input. The figure includes the

SUSP_3V pin from the CS5530 which is used to stop the

external clocks.

Figure 6-4. Stopping SYSCLK During Suspend Mode

SYSCLK

SUSP#

SUSP_3V

SMI Event, Timer or Pin

SUSPA#

(CS5530)

GXM Datasheet(PDF) 178 Page - National Semiconductor (TI)