at89c51re2-slsem ATMEL Corporation, at89c51re2-slsem Datasheet - Page 15

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

Figure 3. Mode Switching Waveforms
7663B–8051–03/07
XTAL1
XTAL1:2
X2 bit
CPU clock
STD Mode
The X2 bit in the CKCON0 register (see Table 14) allows a switch from 12 clock periods
per instruction to 6 clock periods and vice versa. At reset, the speed is set according to
X2 bit of the Fuse Configuration Byte (FCB). By default, Standard mode is active. Set-
ting the X2 bit activates the X2 feature (X2 mode).
The T0X2, T1X2, T2X2, UartX2, PcaX2, and WdX2 bits in the CKCON0 register (See
Table 14.) and SPIX2 bit in the CKCON1 register (see Table 15) allows a switch from
standard peripheral speed (12 clock periods per peripheral clock cycle) to fast periph-
eral speed (6 clock periods per peripheral clock cycle). These bits are active only in X2
mode.
F
OSC
X2 Mode
STD Mode
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