Rainbow Electronics T89C51CC02 - Manual (Page 15)

Rev.A - May 17, 2001 15
Preliminary
T89C51CC02
Figure 4. Mode Switching Waveforms
The X2 bit in the CKCON register (See Table 5) allows switching from 12 clock cycles per instruction to 6 clock
cycles and vice versa. At reset, the standard speed is activated (STD mode). Setting this bit activates the X2 feature
(X2 mode).
CAUTION
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.
XTAL2
XTAL1
CPU clock
X2 bit
X2 Mode STD Mode STD Mode