TS80C54_14 Datasheet, PDF (9/62 Pages) ATMEL Corporation – Programmable Clock Out and Up/Down Timer/Counter 2

AT/TS8xC54/8X2
Figure 6-2. Mode Switching Waveforms
XTAL1
XTAL1:2
X2 bit
CPU clock
STD Mode
X2 Mode
STD Mode
The X2 bit in the CKCON register (See Table 6-1.) allows to switch 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 X2 mode, user must be aware that
all peripherals using clock frequency as time reference (UART, timers) will have their time refer-
ence divided by two. For example a free running timer generating an interrupt every 20 ms will
then generate an interrupt every 10 ms. UART with 4800 baud rate will have 9600 baud rate.
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4431E–8051–04/06