AT89C51AC3-RDTIM datasheet(75/140 Pages) ATMEL

75 / 140 page

AT89C51AC3

4383D–8051–02/08

Programmable Clock-

Output

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

tor (See Figure 41). The input clock increments TL2 at frequency FOSC/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 (FOSC/2

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.

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.

Figure 41. Clock-Out Mode

Clock

OutFrequency

–

2clock

65536

RCAP

–

RCAP

⁄

(

)

-----------------------------------------------------------------------------------------

EXEN2

EXF2

OVERFLOW

T2EX

TH2

(8-bit)

TL2

(8-bit)

TIMER 2

RCAP2H

(8-bit)

RCAP2L

(8-bit)

T2OE

T2CON reg

T2MOD reg

INTERRUPT

TR2

T2CON.2

FT2

CLOCK

Toggle

AT89C51AC3-RDTIM Datasheet(PDF) 75 Page - ATMEL Corporation

AT89C51AC3-RDTIM Datasheet(HTML) 75 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL