Rainbow-electronics T89C51CC01 Bedienungsanleitung PDF herunterladen (Seite 62)

T89C51CC01

Rev. D – 17-Dec-01

Figure 27. Auto-Reload Mode Up/Down Counter

13.2 Programmable

Clock-Output

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

tor (See Figure 28). The input clock increments TL2 at frequency F

OSC

/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 depending on the

system oscillator frequency and the value in the RCAP2H and RCAP2L registers:

For a 16 MHz system clock in x1 mode, timer 2 has a programmable frequency range of

61 Hz (F

OSC

16)

to 4 MHz (F

OSC

/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 different depending on the application.

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

(DOWN COUNTING RELOAD VALUE)

TF2

EXF2

TH2

(8-bit)

TL2

(

8-bit)

RCAP2H

(8-bit)

RCAP2L

(8-bit)

FFh

(8-bit)

FFh

(8-bit)

TOGGLE

(UP COUNTING RELOAD VALUE)

TIMER 2

INTERRUPT

T2CONreg

T2EX:

1=UP

2=DOWN

CT/2

T2CON.1

TR2

T2CON.2

FT2

CLOCK

see section “Clock”

Clock OutFrequency–

FT2clock

4 65536 RCAP2H– RCAP2L⁄()×

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