80C54 Ver la hoja de datos (PDF) - Atmel Corporation

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80C54

8-bit CMOS Microcontroller 16/32 Kbytes ROM/OTP

Atmel Corporation 

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.

9

4431E–8051–04/06

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