HD6417021 Hitachi Semiconductor, HD6417021 Datasheet - Page 179

• Manufacturer Part Number: HD6417021
• Description: SuperH RISC engine
• Manufacturer: Hitachi Semiconductor

For the signal output shown by solid lines, DRAM data may not be held. Therefore, when DRAM
data must be held after reset, take one of the coutermeasures described as follows.
1. When resetting manually, do this in watchdog timer (WDT) condition.
2. Even if the Low width of RAS becomes as short as 1.5 tcyc as shown above, use with a
3. Even in case the Low width of RAS has become 1.5 tcyc, proceed by using the external circuit
A0 to A21
A0 to A21
frequency that satisfies the DRAM standard (tRAS).
so that a RAS signal with a Low width of 2.5 tcyc is input in the DRAM (in case the Low
width of RAS is higher than 2.5 tcyc, operate so that the current waveform is input in the
DRAM).
RES
RAS
CAS
RES
RAS
CAS
CK
RD
RD
CK
RES latch
timing
RES latch
Figure 8.40 Long - pitch Mode Read (1)
Figure 8.41 Long - pitch Mode Read (2)
timing
Manual reset
Manual reset
Tp
Tp
Row address
Row address
Tr
Tr
Colum address
FFFF
Tc1
Tc1
FFFF
Tc2
Tc2
HITACHI 163