at89c51re2-slsem ATMEL Corporation, at89c51re2-slsem Datasheet - Page 16

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

16
AT89C51RE2
Table 14. CKCON0 Register
CKCON0 - Clock Control Register (8Fh)
Reset Value = X000 000’HSB. X2’b (See “Fuse Configuration Byte : FCB”)
Not bit addressable
Number
Bit
7
-
7
6
5
4
3
2
1
0
Mnemonic Description
PCAX2
SIX2_0
WDX2
WDX2
T2X2
T1X2
T0X2
Bit
X2
6
-
Reserved
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
T0X2
1
7663B–8051–03/07
X2
0