UPD784938 Datasheet, PDF (629/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 24 LOCAL BUS INTERFACE FUNCTION
24.3.1 Control registers
(1) Refresh mode register (RFM)
RFM is an 8-bit register that controls the pseudo-static RAM refresh cycle and switching to self-refresh operations.
RFM can be read or written to with an 8-bit manipulation instruction or bit manipulation instruction. The RFM format
is shown in Figure 24-15.
RESET input clears RFM to 00H and sets the REFRQ pin to port mode, so that it operates as the alternate-function
P67 pin.
Figure 24-15. Refresh Mode Register (RFM) Format
7
6
RFM RFLV 0
5
4
3
0 RFEN 0
2
1
0 Address After reset R/W
0 RFT1 RFT0 0FFCCH 00H R/W
RFT1 RFT0
fCLK = 12.58 MHz
Refresh Pulse Output Cycle
Specification
0
0 32/fCLK^Note (2.5 µs)
0
1 64/fCLK (5.1 µs)
1
0 128/fCLK (10.2 µs)
1
1 256/fCLK (20.3 µs)
Note fCLK: Internal system clock frequency
RFLV RFEN REFRQ Pin Output Control
×
0 Port mode
0
1 Self-refresh operation
(REFRQ low level)
1
Refresh pulse output enabled
Remark ×: 0 or 1
Caution The refresh function cannot be used when the bus hold function is used. In this case, ensure that
refreshing is specified as disabled.
Preliminary User’s Manual U13987EJ1V0UM00
629