Rainbow-electronics T89C51CC02 Manual de usuario descargar pdf (Pagina 59)

Rev.A - May 17, 2001 59

Preliminary

T89C51CC02

Figure 45. Auto-Reload Mode Up/Down Counter

13.3. Programmable Clock-Output

In clock-out mode, timer 2 operates as a 50%-duty-cycle, programmable clock generator (See Figure 46). 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:

NOTE: X2 bit is located in CKCON register.

In X2 mode, F

OSC

XTAL

. In standard mode, F

OSC

XTAL

/2.

For a 16 MHz system clock, 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.

(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

Clock OutFrequency–

osc

4 65536 RCAP2H– RCAP2L⁄()×

--------------------------------------------------------------------------------------=

1 2 ... 54 55 56 57 58 59 60 61 62 63 64 ... 136 137

T89C51CC02 1

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