
iiBusModuLes:sdRaMContRoLLeR(sdRaMC)
ii-4-8
ePson
s1C33L17teChniCaLManuaL
ii.4.1.4sdRaMCoperatingClockandsdRaMClock
operatingclockofthesdRaMC
The SDRAMC is clocked by the following clocks generated by the CMU.
For details on how to set and control the clocks, see Section III.1, “Clock Management Unit (CMU).”
The SDRAMC operating clock supply to the SDRAMC is disabled by default setting. Each clock supply can be
controlled in the CMU. Use the respective control bits to turn on only the required clocks to reduce the amount
of power consumed on the chip.
1.sdaPP_CPu_CLKclock
This is the MCLK clock used for interfacing between the CPU and SDRAMC. Turn this clock on when
using the SDRAMC. The clock supply can be controlled by SDAPCPU_CKE (D6/0x301B00).
sdaPCPu_CKe:SDRAMCCPUAPPClockControlBitintheGatedClockControlRegister0
(D6/0x301B00)
Furthermore, the SDAPP_CPU_CLK can automatically be stopped in HALT mode. By setting
SDAPCPU_HCKE (D7/0x301B00) to 0, the SDAPP_CPU_CLK stops when the CPU enters HALT mode
and it resumes when the CPU exits HALT mode.
sdaPCPu_hCKe:SDRAMCCPUAPPClockControl(HALT)BitintheGatedClockControlRegister0
(D7/0x301B00)
2.sdaPP_LCdC_CLKclock
This is the MCLK clock used for interfacing between the LCDC and SDRAMC. Turn this clock on when
using the SDRAM as the video RAM. The clock supply can be controlled by SDAPLCDC_CKE (D5/
0x301B00).
sdaPLCdC_CKe:SDRAMCLCDCAPPClockControlBitintheGatedClockControlRegister0
(D5/0x301B00)
3.ClocksforsdRaMinterfaceandinstruction/dataqueuebuffers
The SDRAMC inputs the OSC_W clock (source clock for MCLK) to operate the SDRAM interface. Also
this clock is used as SDCLK (SDRAM synchronous clock). So the SDRAM can be accessed using a clock
two times faster than the CPU clock when MCLK is generated by dividing OSC_W by 2.
note: TheSDCLKisoutputfromtheSDCLKPin(P21)aftertheChipreset.Iftheoperatingclock(SDCLK)
isstoppedwhiletheSDRAMisbeingaccessed,asystemfailuremayoccurduetostoppageof
theSDRAMoperationinuncontrolledstatus.ThefollowingoperationsstoptheSDCLK,therefore,
donotperformtheseoperationswhentheSDRAMmaybeaccessed.
SettingtheS1C33L17inSLEEPstatus
SwitchingtheP21portfunctionfromSDCLKoutputtogeneral-purposeinput/output
BesidestheCPU,theDMAcontroller(whenDMAtransferfrom/totheSDRAMisenabled)and
theLCDcontroller(whenSDRAMisconfiguredastheVRAMfortheLCDC)accesstheSDRAM.
Inthiscase,beforeperforminganaboveoperation,disabletheDMAtransferandtheLCDCso
thattheSDRAMwillnotbeaccessed.