AT83C51RB2-RLTIM View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT83C51RB2-RLTIM

80C51 High Performance ROM 8-bit Microcontroller

Atmel Corporation 

AT80C51RD2/AT83C51Rx2

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

FCLK PERIPH

:6

T2

0

1

C/T2

T2CON

TR2

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 TH2

(8-bit) (8-bit)

TF2

T2CON

TIMER 2

INTERRUPT

Programmable Clock-

Output

RCAP2L RCAP2H

(8-bit)

(8-bit)

(UP COUNTING RELOAD VALUE)

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

erator (see Figure 7). 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---2I--P-H--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.

19

4113B–8051–03/05

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