STC89C53RC datasheet(106/165 Pages) STC

106 / 165 page

If Timer 2 in Programmabel Clock Out mode, some operations as shown below should be done:

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 the RCAP2H and RCAP2L registers.

Enter the same reload value as the initial value in the TH2 and TL2 registers.

Set TR2 bit in T2CON register to start the Timer 2.

•

Timer 2 Interrupt

T2EX Pin (P1.1)

EXF2

Transition

Detector

control

EXEN2

SYSclk

control

T2 Pin (P1.0)

MCU in 12T mode

MCU in 6T mode

TL2

(8 Bits)

RCAP2L

÷12

÷6

TR2

TH2

(8 Bits)

RCAP2H

C/T2

÷2

T2OE

Timer 2 in Programmable Clock Output Mode

Programmable Clock Output Mode

The STC89xx seires is able to generate a programmable clock output on P1.0. When T2OE bit is set and C//T2

bit is cleared, Timer 2 overflow pulse will generate a 50% duty clock and output that to P1.0. The frequency of

clock-out is calculated according to the following formula.

Baud Rate=

SYSclk

n×[65536 - (RCAP2H, RCAP2L)

when MCU in 12T mode, n=4; when MCU in 6T mode, n=2.

Note Timer 2 overflag, TF2 will always not be set in this mode.

The input clock, SYSclk/2, increments the 16-bit timer (TH2, TL2). The timer repeatedly counts to overflow from

a loaded value. Once overflows occur, the contents of (RCAP2H, RCAP2L) are loaded into (TH2, TL2) for the

consecutive counting. In the clock-out mode, Timer2 rollovers will not generate an interrupt. This is similar to

when Timer 2 is used as a baud-rate generator. It is possible to use Timer 2 as a baud rate generator and a clock

generator simultaneously. Note, however, that the baud-rate and the clock-out frequency depend on the same

overflow rate of Timer 2.The following figure shows the Timer 2 in programmable clock output mode.

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