7 ClOCK GeneRaTOR (ClG)
S1C17624/604/622/602/621 TeChniCal Manual
Seiko epson Corporation
7-11
D1
hSClKSel: high-speed Clock Select Bit
Selects the high-speed clock (HSCLK).
1 (R/W): OSC3
0 (R/W): IOSC (default)
note: Both the IOSC and OSC3 oscillators must be active when selecting HSCLK. Otherwise,
HSCLK will not be switched, even when HSCLKSEL is written to, and the HSCLKSEL value
will remain unchanged.
D0
ClKSRC: System Clock Source Select Bit
Selects the system clock source.
1 (R/W): OSC1
0 (R/W): HSCLK (default)
HSCLK (IOSC or OSC3) is selected for normal (high-speed) operations. If the HSCLK clock is not
required, OSC1 can be set as the system clock and HSCLK (IOSC or OSC3) stopped to reduce current
consumption.
notes: • Both OSC1 and HSCLK must be operating when the system clock is selected (OSC1 or
HSCLK). Otherwise, the system will not switch system clocks, even when CLKSRC is written
to, and the CLKSRC value will remain unchanged. Furthermore, the system clock switching
operation takes a minimum one HSCLK cycle to maximum one OSC1 cycle. Table 7.9.2 lists
the combinations of clock operating states and register settings enabling system clock (OSC1
or HSCLK) selection.
9.2 System Clock Switching (OSC1
Table 7.
↔
HSCLK) Conditions
iOSC
OSC3
OSC1
hSClKSel
System clock
On
On
On
*
IOSC/OSC3 or OSC1
On
Off
On
0
IOSC or OSC1
Off
On
On
1
OSC3 or OSC1
• When switching the HSCLK source (IOSC
↔
OSC3), always make sure that PCKEN[1:0]/
CLG_PCLK register is set to 0x3 before writing to HSCLKSEL.
• The oscillator circuit selected as the system clock source cannot be turned off.
• Continuous write/read access to CLKSRC is prohibited. At least one instruction unrelated to
CLKSRC access must be inserted between the write and read instructions.
• Canceling HALT/SLEEP mode does not change the clock status configured before the chip
entered HALT/SLEEP mode.
Oscillation Control Register (OSC_CTl)
Register name address
Bit
name
Function
Setting
init. R/W
Remarks
Oscillation
Control Register
(OSC_CTl)
0x5061
(8 bits)
D7–6 iOSCWT[1:0] IOSC wait cycle select
IOSCWT[1:0]
Wait cycle
0x0 R/W
0x3
0x2
0x1
0x0
8 cycles
16 cycles
32 cycles
64 cycles
D5–4 OSC3WT[1:0] OSC3 wait cycle select
OSC3WT[1:0]
Wait cycle
0x0 R/W
0x3
0x2
0x1
0x0
128 cycles
256 cycles
512 cycles
1024 cycles
D3
–
reserved
–
–
–
0 when being read.
D2
iOSCen
IOSC enable
1 Enable
0 Disable
1
R/W
D1
OSC1en
OSC1 enable
1 Enable
0 Disable
0
R/W
D0
OSC3en
OSC3 enable
1 Enable
0 Disable
0
R/W
D[7:6]
iOSCWT[1:0]: iOSC Wait Cycle Select Bits
An oscillation stabilization wait time is set to prevent malfunctions due to unstable clock operations at
the start of IOSC oscillation.