Under
development
Preliminary Specifications REV.B3
Specifications in this manual are tentative and subject to change.
Mitsubishi Microcomputers
M32C/83 group
SINGLE-CHIP 16/32-BIT CMOS MICROCOMPUTER
DRAM Controller
303
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 1.28.1 shows the functions of the DRAM controller.
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 1.28.1 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.
(Note 1)
Function
DRAM Control register
Bit name
Bit
symbol
Symbol
Address
When reset
DRAMCONT
004016
Indeterminate
RW
AR1
AR2
DRAM space select bit
WT
AR0
SREF
Note 1: After reset, the content of this register is indeterminate. DRAM controller starts operation after
writing to this register.
Note 2: The number of cycles with 2 waits is 3-2-2. With 1 wait, it is 2-1-1.
Note 3: When you set to "1", both RAS and CAS change to "L". When you set to "0", RAS and CAS
change to "H" and then normal operation (read/write, refresh) is resumed. In stop mode, there is
no control.
Note 4: Set the bus width using the external data bus width control register (address 000B16). When
selecting 8-bit bus width, CASH is indeterminate.
Self-refresh mode bit
(Note 3)
0 : Two wait
1 : One wait
b3 b2 b1
0 0 0 : DRAM ignored
0 0 1 : Must not be set
0 1 0 : 0.5MB
0 1 1 : 1MB
1 0 0 : 2MB
1 0 1 : 4MB
1 1 0 : 8MB
1 1 1 : Must not be set
0 : Self-refresh OFF
1 : Self-refresh ON
Nothing is assigned. When write, set to "0".
When read, their contents are indeterminate.
Wait select bit
(Note 2)
b7
b6
b5
b4
b3
b2
b1
b0
Table 1.28.1. DRAM Controller Functions
Figure 1.28.1. DRAM control register