at89c51re2-slsem ATMEL Corporation, at89c51re2-slsem Datasheet - Page 79

• Manufacturer Part Number: at89c51re2-slsem
• Description: At89c51re2 8-bit Flash Microcontroller
• Manufacturer: ATMEL Corporation

Programmable Clock-
Output
62
AT89C51RE2
Figure 12. Auto-Reload Mode Up/Down Counter (DCEN = 1)
In the clock-out mode, Timer 2 operates as a 50%-duty-cycle, programmable clock gen-
erator (See Figure 13). The input clock increments TL2 at frequency F
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:
For a 16 MHz system clock, Timer 2 has a programmable frequency range of 61 Hz
(F
T2 pin (P1.0).
Timer 2 is programmed for the clock-out mode as follows:
•
•
•
•
•
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.
Clock O
CLK PERIPH
F
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.
CLK PERIPH
– utFrequency
/2
16
)
to 4 MHz (F
=
-------------------------------------------------------------------------------------------- -
4
CLK PERIPH
×
:
6
(
65536 RCAP2H RCAP2L
(UP COUNTING RELOAD VALUE)
(DOWN COUNTING RELOAD VALUE)
F
/4). The generated clock signal is brought out to
–
T2
CLKPERIPH
RCAP2L
(8-bit)
(8-bit)
(8-bit)
TL2
FFh
T2CON
RCAP2H
C/T2
(8-bit)
(8-bit)
TH2
(8-bit)
0
FFh
1
⁄
T2CON
TR2
)
T2EX:
if DCEN=1, 1=UP
if DCEN=1, 0=DOWN
if DCEN = 0, up counting
T2CON
TOGGLE
TF2
CLK PERIPH
7663B–8051–03/07
T2CON
EXF2
INTERRUPT
TIMER 2
/2.The