6 CLOCK MANAGEMENT UNIT (CMU)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
6-11
Clock Supply Control
6.7
To reduce current consumption on the chip, the CMU provides some gate circuits to disable clock supply.
Core Clock (CCLK)
6.7.1
CCLK
HALT
MCLK
Divider
(1/1–1/8)
7.1.1 CCLK Control Circuit
Figure 6.
The CCLK clock is the C33 PE Core operating clock.
In normal mode, CCLK is always supplied to the C33 PE Core.
When the C33 PE Core executes the halt or slp instruction, the CMU stops supplying the clock to the C33 PE Core
and the C33 PE Core enters a standby (HALT or SLEEP) mode. The CMU resumes the clock supply to the C33 PE
Core when the standby mode is canceled by occurrence of an interrupt.
The CMU module includes a divider to slow down CCLK. To reduce current consumption, operate the C33 PE
Core with the slowest possible clock speed.
CLK_DOWN[1:0]/CCU_CCLKDV register is used to select the clock division ratio. For more information on
CLK_DOWN[1:0], see the “Cache Controller (CCU)” chapter.
7.1.1 Core Clock Division Ratio Selection
Table 6.
CLK_DOWN[1:0]
Division ratio
0x3
1/8
0x2
1/4
0x1
1/2
0x0
1/1
(Default: 0x0)
Bus Clock (BCLK)
6.7.2
BCLK
BCLK_EN
HALT
MCLK
7.2.1 BCLK Control Circuit
Figure 6.
The BCLK clock is used to operate the modules listed below.
• IVRAM (Area 3)
• DSTRAM (Area 3)
• SRAM controller (SRAMC)
• SDRAM controller (SDRAMC)
• DMA controller (DMAC)
• LCD controller (LCDC) bus interface
• Clock management unit (CMU) registers
• Bus arbiters
BCLK is required for bus and memory operations, therefore, it is always supplied to the modules listed above in
normal mode.
However, the BCLK supply in HALT mode can be disabled using BCLK_EN/CMU_CLKCTL register if the
LCDC and DMA do not need bus operations.
To stop BCLK in HALT mode, set BCLK_EN to 0. The CMU stops supplying BCLK when the halt instruction is
executed. The CMU resumes the clock supply when the HALT mode is canceled.
To supply BCLK in HALT mode, set BCLK_EN to 1 (default). The modules listed above operates even in HALT
mode.
BCLK stops in SLEEP mode (when the slp instruction is executed) regardless of the BCLK_EN set value.