AT89C51RC2-3CSCM(2003) 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

AT89C51RC2-3CSCM
(Rev.:2003)

8-bit Microcontroller with 16K/32K Bytes Flash

Atmel Corporation 

AT89C51RB2/RC2

Figure 8. Auto-Reload Mode Up/Down Counter (DCEN = 1)

FCLK PERIPH

:6

0

1

T2

C/T2

TR2

T2CON

T2CON

(DOWN COUNTING RELOAD VALUET) 2EX:

FFh FFh

if DCEN = 1, 1 = UP

(8-bit) (8-bit)

if DCEN = 1, 0 = DOWN

if DCEN = 0, up counting

TOGGLE T2CON

EXF2

TL2

(8-bit)

TH2

(8-bit)

TF2

T2CON

TIMER 2

INTERRUPT

RCAP2L RCAP2H

(8-bit)

(8-bit)

(UP COUNTING RELOAD VALUE)

Programmable Clock-out

Mode

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

erator (see Figure 9). The input clock increments TL2 at frequency FCLK PERIPH/2. The

timer repeatedly counts to overflow from a loaded value. At overflow, the contents of

RCAP2H and RCAP2L registers 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----F-–---C-R---L--C-K---P-A---E-P---R-2--I--HP----H--⁄--R-----C-----A----P----2----L----)-

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

(FCLK PERIPH/216) to 4 MHz (FCLK PERIPH/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.

It is possible to use Timer 2 as a baud rate generator and a clock generator simulta-

neously. For this configuration, the baud rates and clock frequencies are not

independent since both functions use the values in the RCAP2H and RCAP2L registers.

25

4180B–8051–04/03

Share Link: