10 SDRAM CONTROLLER (SDRAMC)
10-14
Seiko Epson Corporation
S1C33L26 TECHNICAL MANUAL
Power-Down Mode
10.5.6
The S1C33L26 supports two power-down modes for the C33 PE Core (HALT and SLEEP).
HALT mode
The SDRAM clock will be supplied in HALT mode, if it is not disabled in normal mode.
The SDRAM clock can be stopped before executing the halt instruction by controlling the CMU. To maintain
data in the SDRAM during HALT status with no SDRAM clock supplied, place the SDRAM in self-refresh
mode by setting SELEN/SDRAMC_REF register to 1 before disabling the SDRAM clock supply.
SLEEP mode
In SLEEP mode, the SDRAM can be turned off to reduce power consumption by the following procedure:
1. If the CPU runs with the program stored in the SDRAM, it must be changed to a program located in the
built-in RAM or a memory other than the SDRAM.
2. Turn the SDRAM power off.
3. Switch the ports used for the SDRAM to general-purpose I/O ports.
4. Drive the data and address buses to low.
5. Set SDON/SDRAMC_INIT register to 0 to disable the SDRAMC.
6. Execute the slp instruction.
Perform the following procedure when the CPU wakes up from SLEEP status:
1. The CPU wakes up from SLEEP status.
2. Configure the port functions for the SDRAM.
3. Release the data and address buses from forced low driving.
4. Turn the SDRAM power on.
5. Wait at least 100 or 200 µs for the SDRAM to be stabilized, according to the SDRAM specifications.
6. Set SDON/SDRAMC_INIT register to 1 to enable the SDRAMC.
7. Initialize the SDRAMC.
Data Queue Buffer (DQB)
10.6
The bus controller of the S1C33L26 also includes a data queue buffer (DQB) to increase the C33 PE Core memory
access performance.
SDRAM/
SRAM
interface
External
memory
Data queue
buffer
Read/write
control
To AHB bus
Data input
Data output
Read/write
signals
#WAIT
6.1 Data Queue Buffer
Figure 10.
The DQB is a 4
×
16-bit buffer used as an instruction/data buffer for reading from the SDRAM or the external
memories of the SRAMC.
The DQB acts as a pure read buffer for storing all data read from the SDRAM or external memories of the
SRAMC, regardless of whether the target is an instruction or data. Note that the DQB cannot be disabled.
Table 10.6.1 lists the DQB status corresponding to the bus operation for the SDRAM or the external memories of
SRAMC.