
CHAPTER 5 MEMORY ACCESS CONTROL FUNCTION
236
Preliminary User’s Manual U16031EJ2V1UD
5.3.6 Refresh control function
The V850E/ME2 can generate a refresh cycle. The refresh cycle is set with SDRAM refresh control registers 1, 3,
4, and 6 (RFS1, RFS3, RFS4, RFS6). RFSn corresponds to CSn (n = 1, 3, 4, 6). For example, to connect SDRAM to
CS1, set RFS1.
When another bus master occupies the external bus, the DRAM controller cannot occupy the external bus. In this
case, the DRAM controller issues a refresh request to the bus master by changing the REFRQ signal to active (low
level).
During a refresh operation, the address bus retains the state it was in just before the refresh cycle.
(1) SDRAM refresh control registers 1, 3, 4, 6 (RFS1, RFS3, RFS4, RFS6)
These registers are used to enable or disable a refresh and set the refresh interval. The refresh interval is
determined by the following calculation formula.
Refresh interval (
s) = Refresh count clock (TRCY) × Interval factor
The refresh count clock and interval factor are determined by the RCCn1 and RCCn0 bits and RIN5n to
RIN0n bits, respectively, of the RFSn register.
Note that n corresponds to the register number (1, 3, 4, 6) of SDRAM configuration registers 1, 3, 4, 6 (SCR1,
SCR3, SCR4, SCR6).
These registers can be read or written in 16-bit units.
Caution
Write to the RFS1, RFS3, RFS4, and RFS6 registers after reset, and then do not change the
set values. However, when the SDRAM refresh interval needs to be changed by changing
the CKC register set value (internal system clock (fCLK)), the set value of the RFS1, RFS3,
RFS4, and RFS6 registers can be changed. For details, refer to Caution 2 in 8.3.1 Clock
control register (CKC). Also, do not access an external memory area other than the one for
this initialization routine until the initial settings of the RFS1, RFS3, RFS4, and RFS6
registers are complete. However, it is possible to access external memory areas whose
initialization settings are complete.