AT89C51RE2 Atmel Corporation, AT89C51RE2 Datasheet - Page 123

• Manufacturer Part Number: AT89C51RE2
• Manufacturer: Atmel Corporation

Specifications of AT89C51RE2

• Flash (kbytes): 128 Kbytes
• Max. Operating Frequency: 60 MHz
• Cpu: 8051-12C
• Max I/o Pins: 34
• Spi: 1
• Uart: 2
• Sram (kbytes): 8.25
• Self Program Memory: API
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 4
• Isp: UART/OCD
• Watchdog: Yes

Functional Block Diagram
Figure 46. Functional Oscillator Block Diagram
Prescaler Divider
7663E–8051–10/08
Xtal2
Xtal1
Osc
F
•
•
F
In X2 Mode, for CKRL<>0xFF:
In X1 Mode, for CKRL<>0xFF then:
F
F
OSC
CLK CPU
CPU
CPU
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:
•
•
=
=
: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
AT89C51RE2
Peripheral Clock
CPU Clock
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