at89c51re2-slsem ATMEL Corporation, at89c51re2-slsem Datasheet - Page 124

• Manufacturer Part Number: at89c51re2-slsem
• Description: At89c51re2 8-bit Flash Microcontroller
• Manufacturer: ATMEL Corporation

Functional Block Diagram
Figure 30. Functional Oscillator Block Diagram
Prescaler Divider
7663B–8051–03/07
Xtal2
Xtal1
Osc
F
OSC
:2
Reset
Reset Value = 00X1 0000b Not bit addressable
•
•
F
In X2 Mode, for CKRL<>0xFF:
In X1 Mode, for CKRL<>0xFF then:
F
F
CLK CPU
CPU
CPU
CKCON0
A hardware RESET puts the prescaler divider in the following state:
• CKRL = FFh: F
Any value between FFh down to 00h can be written by software into CKRL register
in order to divide frequency of the selected oscillator:
•
•
CKRL
=
=
X2
0
F
F
F
F
1
CKRL = 00h: minimum frequency
CKRL = FFh: maximum frequency
F
F
CLK CPU
CLK CPU
CLK CPU
CLK CPU
and F
CLKPERIPH
CLKPERIPH
CLK PERIPH
Prescaler-Divider
= F
= F
= F
= F
CLK PERIPH
CLK PERIPH
CLK PERIPH
CLK PERIPH
=
=
8-bit
Reload
CLK CPU
---------------------------------------------- -
2
---------------------------------------------- -
4
×
×
(
(
255 CKRL
255 CKRL
F
F
= F
= F
OSC
OSC
= F
= F
= F
–
–
OSC
OSC
OSC
OSC
CLK PERIPH
CKRL = 0xFF?
/1020 (Standard Mode)
/510 (X2 Mode)
/2 (Standard Mode)
(X2 Mode)
)
)
1
0
= F
OSC
Idle
/2 (Standard C51 feature)
CLK
Periph
CLK
CPU
Peripheral Clock
CPU Clock
107