AT80C51RA2-3CSCV データシートの表示（PDF） - Atmel Corporation

部品番号

コンポーネント説明

メーカー

AT80C51RA2-3CSCV

High Performance 8-bit Microcontrollers

Atmel Corporation 

Figure 6-2. Auto-reload Mode Up/Down Counter (DCEN = 1)

XTAL1

FXTAL

FOSC

(:6 in X2 mode)

:12

0

1

T2

C/T2

TR2

T2CONreg T2CONreg

(DOWN COUNTING RELOAD VALUE)

FFh

FFh

(8-bit) (8-bit)

TL2

TH2

(8-bit) (8-bit)

T2EX:

if DCEN=1, 1=UP

if DCEN=1, 0=DOWN

if DCEN = 0, up

counting

TOGGLE T2CONreg

EXF2

TF2

TIMER 2

INTERRUPT

T2CONreg

RCAP2L RCAP2H

(8-bit)

(8-bit)

(UP COUNTING RELOAD VALUE)

6.2.2

Programmable Clock-Output

In the clock-out mode, timer 2 operates as a 50%-duty-cycle, programmable clock generator

(See Figure 6-3) . The input clock increments TL2 at frequency FOSC/2. The timer repeatedly

counts to overflow from a loaded value. At overflow, the contents of RCAP2H and RCAP2L reg-

isters are loaded into TH2 and TL2. In this mode, timer 2 overflows do not generate interrupts.

The formula gives the clock-out frequency as a function of the system oscillator frequency and

the value in the RCAP2H and RCAP2L registers:

Clock – OutFrequency = -4----×-----(---6---5---5----3---6-----–----R----FC----o-A--s--P-c---2---H------⁄---R----C----A----P----2----L----)

For a 16 MHz system clock, timer 2 has a programmable frequency range of 61 Hz

(FOSC/216) to 4 MHz (FOSC/4). The generated clock signal is brought out to T2 pin (P1.0).

Timer 2 is programmed for the clock-out mode as follows:

• Set T2OE bit in T2MOD register.

• Clear C/T2 bit in T2CON register.

• Determine the 16-bit reload value from the formula and enter it in RCAP2H/RCAP2L

registers.

• Enter a 16-bit initial value in timer registers TH2/TL2. It can be the same as the reload value

or a different one depending on the application.

• To start the timer, set TR2 run control bit in T2CON register.

20 AT/TS8xC51Rx2

4188F–8051–01/08

Share Link: