6 CLOCK MANAGEMENT UNIT (CMU)
6-14
Seiko Epson Corporation
S1C33L26 TECHNICAL MANUAL
SDCLK is supplied even in HALT mode when SDCLK_EN is set to 1. To stop the clock supply in HALT mode, set
SDCLK_EN to 0 before executing the halt instruction.
In SLEEP mode (when the slp instruction is executed), SDCLK stops even if SDCLK_EN is set to 1.
SYSCLK is directly fed to the SDCLK pin used to connecting an external SDRAM. In normal or HALT mode, the
SDCLK pin always outputs the clock. In SLEEP mode, the SDCLK pin stops supplying the clock.
USB Clocks (USBCLK, USBREGCLK)
6.7.7
USBCLK
USBCLK_EN
OSC3
USBREGCLK
USBREGCLK_EN
MCLK
7.7.1 USBCLK/USBREGCLK Control Circuit
Figure 6.
The USBCLK clock is the USB operating clock supplied to the USB function controller. Use a 48 MHz ceramic
resonator for the OSC3 oscillator circuit when using the USB function. USBCLK_EN/CMU_CLKCTL register is
used for clock supply control. The default setting of USBCLK_EN is 0, which disables the clock supply. Enable the
clock supply by setting USBCLK_EN to 1 before the USB function controller can be used.
USBCLK is supplied even in HALT mode when USBCLK_EN is set to 1. To stop the clock supply in HALT mode,
set USBCLK_EN to 0 before executing the halt instruction.
In SLEEP mode (when the slp instruction is executed), USBCLK stops even if USBCLK_EN is set to 1.
The USBREGCLK clock is the clock for accessing the USB registers. USBREGCLK_EN/CMU_CLKCTL register
is used for clock supply control. The default setting of USBREGCLK_EN is 0, which disables the clock supply.
Enable the clock supply by setting USBREGCLK_EN to 1 before the USB registers can be accessed.
USBREGCLK is supplied even in HALT mode when USBREGCLK_EN is set to 1. To stop the clock supply in
HALT mode, set USBREGCLK_EN to 0 before executing the halt instruction.
In SLEEP mode (when the slp instruction is executed), USBREGCLK stops even if USBREGCLK_EN is set to 1.
Note: When accessing the USB registers, the USBCLK clock must be supplied to the USB function con-
troller in addition to USBREGCLK.
Clock External Output (CMU_CLK)
6.8
An internally generated clock can be output from the CMU_CLK pin to external devices.
The output clock can be selected from among 11 clocks using CMU_CLKSEL[4:0]/CMU_CMUCLK register.
8.1 CMU_CLK Selections
Table 6.
CMU_CLKSEL[4:0]
CMU_CLK
0xf–0xb
Reserved
0xa
OSC/32
0x9
OSC/16
0x8
OSC/8
0x7
OSC/4
0x6
OSC/2
0x5
OSC/1
0x4
LCLK
0x3
BCLK
0x2
PLL
0x1
OSC1
0x0
OSC3
(Default: 0x0)
CMU_CLK can be selected at any time. However, switching over the clocks creates hazards.
Note: Settings other than those listed in Table 6.8.1 are reserved for testing. Do not set undescribed val-
ues to CMU_CLKSEL[4:0] as undesired clocks may output.