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7 ClOCK GeneRaTOR (ClG)
7-6
Seiko epson Corporation
S1C17153 TeChniCal Manual
(Rev. 1.0)
• When SLEEP mode is canceled, the OSC3B oscillator circuit is turned on (OSC3BEN = 1)
and is used as the system clock source (CLKSRC[1:0] = 0x0) regardless of the system clock
configured before the chip entered SLEEP mode.
Canceling HALT mode does not change the clock status configured before the chip entered
HALT mode.
CPu Core Clock (CClK) Control
7.5
The CLG module includes a clock gear to slow down the system clock to send to the S1C17 Core. To reduce cur-
rent consumption, operate the S1C17 Core with the slowest possible clock speed. The
halt
instruction can be ex-
ecuted to stop the clock supply from the CLG to the S1C17 Core for power savings.
OSC3B
OSC1A
CCLK
Clock gear
(1/1–1/8)
Gate
S1C17 Core
Gear selection
System clock
HALT
5.1 CCLK Supply System
Figure 7.
Clock gear settings
CCLKGR[1:0]/CLG_CCLK register is used to select the gear ratio to reduce system clock speeds.
5.1 CCLK Gear Ratio Selection
Table 7.
CClKGR[1:0]
Gear ratio
0x3
1/8
0x2
1/4
0x1
1/2
0x0
1/1
(Default: 0x0)
Clock supply control
The CCLK clock supply is stopped by executing the
halt
instruction. Since this does not stop the system
clock, peripheral modules will continue to operate.
HALT mode is cleared by resetting, NMI, or other interrupts. The CCLK supply resumes when HALT mode is
cleared.
Executing the
slp
instruction suspends system clock supply to the CLG, thereby halting the CCLK supply as
well. Clearing SLEEP mode with an external interrupt restarts the system clock supply and the CCLK supply.
Peripheral Module Clock (PClK) Control
7.6
The CLG module also controls the clock supply to peripheral modules.
The system clock is used unmodified for the peripheral module clock (PCLK).
Internal peripheral modules
Gate
On/Off control
PCLK
System clock
OSC3B
OSC1A
6.1 Peripheral Module Clock Control Circuit
Figure 7.
Clock supply control
PCLK supply is controlled by PCKEN[1:0]/CLG_PCLK register.
6.1 PCLK Control
Table 7.
PCKen[1:0]
PClK supply
0x3
Enabled (on)
0x2
Setting prohibited
0x1
Setting prohibited
0x0
Disabled (off)
(Default: 0x3)