at89c51rd2-smsum ATMEL Corporation, at89c51rd2-smsum Datasheet - Page 16

• Manufacturer Part Number: at89c51rd2-smsum
• Description: 8-bit Flash Microcontroller
• Manufacturer: ATMEL Corporation

6.2
Figure 6-1.
6.2.1
16
Xtal2
Xtal1
Functional Block Diagram
AT89C51RD2/ED2
Prescaler Divider
Functional Oscillator Block Diagram
Osc
F
F
In X2 Mode, for CKRL<>0xFF:
In X1 Mode, for CKRL<>0xFF then:
F
F
OSC
CLK CPU
• A hardware RESET puts the prescaler divider in the following state:
• Any value between FFh down to 00h can be written by software into CKRL register in order to
CPU
CPU
divide frequency of the selected oscillator:
• CKRL = FFh: F
•
•
=
=
:2
Reset
F
F
F
F
CKRL = 00h: minimum frequency
CKRL = FFh: maximum frequency
F
F
CLK CPU
CLK CPU
CLK CPU
CLK CPU
and F
CLKPERIPH
CLKPERIPH
CKCON0
CKRL
CLK PERIPH
X2
0
1
= F
= F
= F
= F
CLK PERIPH
CLK PERIPH
CLK PERIPH
CLK PERIPH
=
=
CLK CPU
---------------------------------------------- -
2
---------------------------------------------- -
4
Prescaler-Divider
×
×
(
(
255 CKRL
255 CKRL
F
F
8-bit
= F
= F
OSC
OSC
= F
= F
= F
–
–
Reload
OSC
OSC
OSC
OSC
CLK PERIPH
/1020 (Standard Mode)
/510 (X2 Mode)
/2 (Standard Mode)
(X2 Mode)
)
)
CKRL = 0xFF?
= F
OSC
1
0
/2 (Standard C51 feature)
Idle
CLK
Periph
CLK
CPU
Peripheral Clock
CPU Clock
4235J–8051–01/08