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Preliminary Specifications REV.D
Specifications in this manual are tentative and subject to change.
Mitsubishi Microcomputers
M16C/80 group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
DRAM Controller
182
DRAM Controller
There is a built in DRAM controller to which it is possible to connect between 512 Kbytes and 8 Mbytes of
DRAM. Table 1.25.1 shows the functions of the DRAM controller.
Table 1.25.1. DRAM Controller Functions
DRAM space
512KB, 1MB, 2MB, 4MB, 8MB
Bus control
2CAS/1W
Refresh
________
CAS before RAS refresh
Self refresh-compatible
Function modes
EDO-compatible, fast page mode-compatible
Waits
1 wait or 2 waits, programmable
To use the DRAM controller, use the DRAM space select bit of the DRAM control register (address 004016)
to specify the DRAM size. Figure 1.25.1 shows the DRAM control register.
The DRAM controller cannot be used in external memory mode 3 (bits 1 and 2 at address 000516 are “112”).
Always use the DRAM controller in external memory modes 0, 1, or 2.
When the data bus width is 16-bit in DRAM area, set "1" to R/W mode select bit (bit 2 at address 000416).
Set wait time between after DRAM power ON and before memory processing, and processing necessary
for dummy cycle to refresh DRAM by software.
DRAM control register
Symbol
Address
When reset
DRAMCONT
0004016
Indeterminate (Note 4)
Bit name
Function
Bit symbol
W
R
b7 b6 b5 b4 b3
b2 b1 b0
AR1
WT
AR0
AR2
0 0 0 : DRAM ignored
0 0 1 : Inhibit
0 1 0 : 0.5MB
0 1 1 : 1MB
1 0 0 : 2MB
1 0 1 : 4MB
1 1 0 : 8MB
1 1 1 : Inhibit
b3 b2 b1
DRAM space select bit
Wait select bit (Note 1)
Self-refresh mode bit
(Note 2)
SREF
0 : Two wait
1 : One wait
0: Self-refresh OFF
1: Self-refresh ON
Nothing is assigned.
When write, set "0". When read, the value of these bits is indeterminate.
Note 1: The number of cycles with 2 waits is 3-2-2. With 1 wait, it is 2-1-1.
Note 2: When you set "1", both RAS and CAS change to "L". When you set "0",
RAS and CAS change to "H" and then normal operation (read/write, refresh)
is resumed. In Stop mode, there is no control.
Note 3: Set the bus width using the external data bus width control register (address
000B16). When selecting 8-bit bus width, CASH is indeterminate.
Note 4: After reset, the content of this register is indeterminate.
DRAM controller starts the operation after writing to this register.
Figure 1.25.1. DRAM control register