Datasheet

AT89C51AC3

4383D–8051–02/08

Figure 6. Mode Switching Waveforms

Note: In order to prevent any incorrect operation while operating in the X2 mode, users must be aware that all peripherals using the

clock frequency as a time reference (UART, timers...) will have their time reference divided by two. For example a free running

timer generating an interrupt every 20 ms will then generate an interrupt every 10 ms. A UART with a 4800 baud rate will have

a 9600 baud rate.

XTAL1/2

XTAL1

CPU clock

X2 bit

X2 ModeSTD Mode STD Mode