10 SDRAM CONTROLLER (SDRAMC)
10-2
Seiko Epson Corporation
S1C33L26 TECHNICAL MANUAL
Notes: • Some of the bus control pins listed above are shared with general-purpose I/O ports and they
may be configured for I/O ports at initial reset. Before the SDRAMC signals assigned to these
pins can be used, the functions of these pins must be switched for the SDRAMC by setting
each corresponding port function select bit.
For details on how to switch over the pin functions, see the “I/O Ports (GPIO)” chapter.
• The bus control signals can be pulled up or forcibly driven low via software. For more informa-
tion, see the “I/O Ports (GPIO)” chapter.
SDRAM Clock and Double Frequency Mode
10.3
The SDCLK clock is supplied to the SDRAMC from the CMU for use as the operating clock of the SDRAMC
module as well as the SDRAM clock.
The CMU register can be used to control the clock supply (on/off). When no SDRAM is used, stop the clock.
SDCLK does not stop even in HALT mode. To stop the clock in HALT mode, turn the clock supply off in the CMU
before executing the halt instruction.
SDCLK stops in SLEEP mode.
PCLK2 is also used for accessing the SDRAMC control registers.
For details on how to set and control the clock, refer to the “Clock Management Unit (CMU)” chapter.
Double frequency mode
The SDRAMC supports double frequency mode in which the SDRAM can be operated with a clock two times
faster than the CPU clock. For example, when the CPU runs with a 30 MHz clock, the SDRAM can be oper-
ated with a 60 MHz clock.
To set the SDRAMC in double frequency mode:
(1) Set MCLK (main system clock) to the SYSCLK (= SDCLK) frequency × 1/2.
(2) Set DBF/SDRAMC_APP register to 1.
SDCLK frequency limitations
The SDCLK clock frequency is limited to maximum 72 MHz.
Normal mode:
SDCLK = MCLK
≤
60 MHz
Double frequency mode: SDCLK = 2MCLK
≤
72 MHz, MCLK
≤
36 MHz
Configuration of SDRAM
10.4
SDRAM Area
10.4.1
A #CE7 area (Area 7 or Area 19) is reserved for the SDRAMC. Note that the #CE7 area is configured for an
SRAM area controlled with the SRAMC as the SDRAMC is disabled at initial reset. Therefore, to use the SDRAM,
the #CE7 area must be configured for the SDRAM area by setting SDON/SDRAMC_INIT register to 1.
Note: Setting SDON to 1 overrides the external SRAM access conditions for the #CE7 area set in the
SRAMC.
SDRAM Size and Access Condition Settings
10.4.2
Table 10.4.2.1 lists the conditions related to SDRAM size and timing parameters that the SDRAMC can accommo-
date.