Clock prescaler, Clock control registers, Clock prescaler register – Rainbow Electronics T89C5121 User Manual
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A/T8xC5121
4164G–SCR–07/06
Clock Prescaler
Before supplying the CPU and the peripherals, the main clock is divided by a factor 2 to
30 to reduce the CPU power consumption. This factor is controlled with the CKRL
register.
Table 7. Examples of Factors
Clock Control Registers
Clock Prescaler Register
This register is used to reload the clock prescaler of the CPU and peripheral clock.
Table 8. CKRL Register
CKRL - Clock Reload Register (97h)
Reset Value = XXXX 111Xb
XTAL (MHz)
X2 CPU CKCON0
CKRL Value
Prescaler Factor
F
CLK_CPU,
F
CLK_Periph
(MHz)
16
0 (reset mode)
07h
1
8
16
1 (X2 mode)
07h
1
16
16
1
07h
1
16
16
0
07h
1
8
16
0
06h
2
4
16
1 06h
2
8
7
6
5
4
3
2
1
0
-
-
-
-
CKRL
CKRL
CKRL
-
Bit
Number
Bit
Mnemonic
Description
7 - 4
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
3 - 1
CKRL
Clock Reload Register
Prescaler value
XXXX 000Xb: CKRL=7 and Division factor equals 14
XXXX 110Xb: CKRL=6 and factor equals 2
XXXX 111Xb: CKRL=7 and division factor equals 1
0
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.