AT89C51RE2 Atmel Corporation, AT89C51RE2 Datasheet - Page 15

• 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

7663E–8051–10/08
Table 15. CKCON0 Register
CKCON0 - Clock Control Register (8Fh)
Reset Value = X000 000’HSB. X2’b (See “Fuse Configuration Byte: FCB”)
Not bit addressable
Number
TWIX2
Bit
7
7
6
5
4
3
2
1
0
Mnemonic
WDX2
PCAX2
SIX2_0
TWIX2
WDX2
T2X2
T1X2
T0X2
Bit
X2
6
Description
2-wire cloTBck
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect)
Cleared to select 6 clock periods per peripheral clock cycle.
Set to select 12 clock periods per peripheral clock cycle.
Watchdog Clock
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle.
Set to select 12 clock periods per peripheral clock cycle.
Programmable Counter Array Clock
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle. Set to select 12 clock
periods per peripheral clock cycle.
Enhanced UART0 Clock (Mode 0 and 2)
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle. Set to select 12 clock
periods per peripheral clock cycle.
Timer2 Clock
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle.
Set to select 12 clock periods per peripheral clock cycle.
Timer1 Clock
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle. Set to select 12 clock
periods per peripheral clock cycle.
Timer0 Clock
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle. Set to select 12 clock
periods per peripheral clock cycle.
CPU Clock
Cleared to select 12 clock periods per machine cycle (STD mode) for CPU and all the
peripherals. Set to select 6clock periods per machine cycle (X2 mode) and to enable the
individual peripherals’X2’ bits. Programmed by hardware after Power-up regarding
Hardware Security Byte (HSB), Default setting, X2 is cleared.
PCAX2
5
SIX2_0
4
T2X2
3
T1X2
2
AT89C51RE2
T0X2
1
X2
0
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