at89c51rd2-smsum ATMEL Corporation, at89c51rd2-smsum Datasheet - Page 31

• Manufacturer Part Number: at89c51rd2-smsum
• Description: 8-bit Flash Microcontroller
• Manufacturer: ATMEL Corporation

12.2
4235J–8051–01/08
Programmable
Clock-output
Figure 12-1. Auto-reload Mode Up/Down Counter (DCEN = 1)
In the clock-out mode, Timer 2 operates as a 50% duty-cycle, programmable clock generator
(See Figure 12-2). The input clock increments TL2 at frequency F
edly 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 inter-
rupts. 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
(P1.0).
Timer 2 is programmed for the clock-out mode as follows:
Clock O
• 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
• Enter a 16-bit initial value in timer registers TH2/TL2. It can be the same as the reload value
• To start the timer, set TR2 run control bit in T2CON register.
CLK PERIPH
registers.
or a different one depending on the application.
– utFrequency
F
/2
CLK PERIPH
16
)
to 4 MHz (F
=
-------------------------------------------------------------------------------------------- -
4
×
CLK PERIPH
(
65536 RCAP2H RCAP2L
:
6
F
–
/4). The generated clock signal is brought out to T2 pin
CLKPERIPH
(UP COUNTING RELOAD VALUE)
(DOWN COUNTING RELOAD VALUE)
T2
RCAP2L
(8-bit)
(8-bit)
(8-bit)
TL2
FFh
⁄
T2CON
RCAP2H
C/T2
(8-bit)
(8-bit)
TH2
(8-bit)
0
1
FFh
AT89C51RD2/ED2
)
CLK PERIPH
T2CON
TR2
/2. The timer repeat-
T2EX:
If DCEN = 1, 1 = UP
If DCEN = 1, 0 = DOWN
If DCEN = 0, up counting
T2CON
TOGGLE
TF2
T2CON
EXF2
INTERRUPT
TIMER 2
31