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Oscillators and Clocks
CLKCONCMD (0xC6)
–
Clock Control Command
Bit
Name
Reset
R/W
Description
7
OSC32K
1
R/W
32 kHz clock-source select. Setting this bit initiates a clock-source change only.
CLKCONSTA.OSC32K reflects the current setting. The 16 MHz RCOSC must be
selected as system clock when this bit is to be changed.
0: 32 kHz XOSC
1: 32 kHz RCOSC
6
OSC
1
R/W
System clock-source select. Setting this bit initiates a clock-source change only.
CLKCONSTA.OSC reflects the current setting.
0: 32 MHz XOSC
1: 16 MHz RCOSC
5:3
TICKSPD[2:0]
001
R/W
Timer ticks output setting. Cannot be higher than system clock setting given by OSC
bit setting.
000: 32 MHz
001: 16 MHz
010: 8 MHz
011: 4 MHz
100: 2 MHz
101: 1 MHz
110: 500 kHz
111: 250 kHz
Note that
CLKCONCMD.TICKSPD
can be set to any value, but the effect is
limited by the
CLKCONCMD.OSC
setting; i.e., if
CLKCONCMD.OSC
= 1 and
CLKCONCMD.TICKSPD
= 000,
CLKCONSTA.TICKSPD
reads 001, and the
real
TICKSPD
is 16 MHz.
2:0
CLKSPD
001
R/W
Clock speed. Cannot be higher than system clock setting given by the OSC bit
setting. Indicates current system-clock frequency
000: 32 MHz
001: 16 MHz
010: 8 MHz
011: 4 MHz
100: 2 MHz
101: 1 MHz
110: 500 kHz
111: 250 kHz
Note that
CLKCONCMD.CLKSPD
can be set to any value, but the effect is
limited by
the
CLKCONCMD.OSC
setting; i.e., if
CLKCONCMD.OSC
= 1 and
CLKCONCMD.CLKSPD
= 000,
CLKCONSTA.CLKSPD
reads 001, and the real
CLKSPD
is 16 MHz.
Note also that the debugger cannot be used with a divided system clock. When
running the debugger, the value of
CLKCONCMD.CLKSPD
should be set to 000 when
CLKCONCMD.OSC
= 0 or to 001 when
CLKCONCMD.OSC
= 1.
71
SWRU191C
–
April 2009
–
Revised January 2012
Power Management and Clocks
Copyright
©
2009
–
2012, Texas Instruments Incorporated