AT89C51RB2-RLTCM ATMEL [ATMEL Corporation], AT89C51RB2-RLTCM Datasheet - Page 13

• Manufacturer Part Number: AT89C51RB2-RLTCM
• Description: 8-bit Microcontroller with 16K/ 32K Bytes Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Functional Block
Diagram
Figure 3. Functional Oscillator Block Diagram
Prescaler Divider
4180B–8051–04/03
Xtal2
Xtal1
Osc
F
OSC
:2
Reset
•
•
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
---------------------------------------------- -
2
---------------------------------------------- -
4
CLK CPU
×
×
(
(
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)
AT89C51RB2/RC2
CLK
PERIPH
CLK
CPU
Peripheral Clock
CPU clock
13