
Memory Management
2-3
2.1.1
DRAM Configurations
The élanSC310 microcontroller supports up to 16 Mbyte of on-board DRAM, organized
as one or two memory banks (16-bit data path to memory). The RAS0 and RAS1 signals
enable the banks, while the CAS0L, CAS0H, CAS1L, and CAS1H signals are used to
select the upper and lower sections of each bank. Each bank is 16 bits wide and contains
1, 2, or 4 chips depending on the bit architecture of the memory chips. The following bits
are used to specify the memory size and architecture:
I
Bits 4–2 of the Memory Configuration 1 register at Index 66h
I
Bits 7–6 of the Function Enable 2 register at Index B1h
I
Bit 7 of the Function Enable 3 register at Index B4h
Insight into the mapping of both DRAM configurations can be gained by examining
Table 4-23 on page 4-28 and Table 4-38 on page 4-63. As an example of how to program
the memory configuration, the settings in Table 2-1 on page 2-3 select a 4-Mbyte memory
that is organized into two banks and configured for Enhanced-Page-mode operation.
2.1.2
Refresh and Wait States
The élanSC310 microcontroller supports two memory refresh modes:
I
8254-based DRAM refresh
I
Slow-refresh DRAM
The 8254-based DRAM refresh cannot be selected if power management is performed
because the 8254 clock will be turned off in Suspend mode. Memory refresh needs to
remain enabled since the PMU uses the refresh pulse to synchronize events. The refresh
frequency is under programmer control. See “PMU Control 1 Register (Index A7h)” on
page 4-56 and “Version Register (Index 64h)” on page 4-26.
For example, the settings shown in Table 2-2 on page 2-3 perform the following opera-
tions:
I
Select Slow-Refresh mode for DRAM refreshes. The DRAMs are refreshed at the rate
selected by bits 1 and 0 of the Version register at Index 64h.
I
Select the 32-kHz clock input as the refresh source.
Table 2-1
Memory Initialization Example
Instruction
Ports
Data
Comment
IOW
IOW
022h
023h
B4h
0100 0000
Enable the Memory Configuration 1 register at Index 66h to select
memory configuration.
IOW
IOW
022h
023h
66h
xxx1 0011
Select 4-Mbyte memory configuration (Enhanced Page mode). Note
that bits 6–5 are read only.
Table 2-2
Refresh Initialization Example
Instruction
Ports
Data
Comment
IOW
IOW
022h
023h
A7h
xxxx xx00
Enable slow refresh; select 32-kHz clock for refresh source; disable
refresh during Sleep mode.