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CLOCK CIRCUIT S3C8275X/F8275X/C8278X/F8278X/C8274X/F8274X
7-4
SYSTEM CLOCK CONTROL REGISTER (CLKCON)
The system clock control register, CLKCON, is located in the set 1, at address D4H. It is read/write addressable
and has the following functions:
• Oscillator IRQ wake up function enable/disable
• Oscillator frequency divide-by value
CLKCON register settings control whether or not an external interrupt can be used to trigger a stop mode release
(This is called the "IRQ wake-up" function). The IRQ "wake-up" enable bit is CLKCON.7.
After the main oscillator is activated, and the fxx/16 (the slowest clock speed) is selected as the CPU clock. If
necessary, you can then increase the CPU clock speed to f
xx/8, fxx/2, or fxx/1.
System Clock Control Register (CLKCON)
D4H, Set 1, R/W
LSBMSB .7 .6 .5 .4 .3 .2 .1 .0
Not used for S3C8275X/C8278X/C8274X
(must keep always 0)
Not used for S3C8275X/C8278X/C8274X
(must keep always 0)
Divide-by selection bits for
CPU clock frequency:
00 = fxx/16
01 = fxx/8
10 = fxx/2
11 = fxx/1 (non-divided)
Oscillator IRQ wake-up function bit:
0 = Enable IRQ for main wake up in
power down mode
1 = Disable IRQ for main wake up in
power down mode
Figure 7-7. System Clock Control Register (CLKCON)