H8SLASH3028F datasheet(192/923 Pages) RENESAS

192 / 923 page

Rev. 2.00, 09/03, page 162 of 890

When RAS down mode is selected, the CAS-before-RAS refresh function provided with this

DRAM interface must always be used as the DRAM refreshing method. When a refresh

operation is performed, the

RAS signal goes high immediately beforehand. The refresh

interval setting must be made so that the maximum DRAM

RAS pulse width specification is

observed.

When the self-refresh function is used, the RDM bit must be cleared to 0, and RAS up mode

selected, before executing a SLEEP instruction in order to enter software standby mode.

Select RAS down mode again after exiting software standby mode.

Note that RAS down mode cannot be used when

HWR and LWR are selected for UCAS and

LCAS, a device other than DRAM is connected to external space, and HWR and LWR are

used as write strobes.

• RAS Up Mode

To select RAS up mode, clear the RDM bit to 0 in DRCRA. Each time access to DRAM space

is interrupted and another space is accessed, the

RAS signal returns to the high level. Burst

operation is only performed if DRAM space is continuous. Figure 6.25 shows an example of

the timing in RAS up mode.

A23 to A0

CSn (RAS)

Tc2

D15 to D0

Tc1

Tc2

Tc1

PB4/PB5

(

UCAS/LCAS)

Note: n = 2 to 5

DRAM access

External space

access

Figure 6.25 Example of Operation Timing in RAS Up Mode

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