AT89C51RE2 Atmel Corporation, AT89C51RE2 Datasheet - Page 78

• Manufacturer Part Number: AT89C51RE2
• Manufacturer: Atmel Corporation

Specifications of AT89C51RE2

• Flash (kbytes): 128 Kbytes
• Max. Operating Frequency: 60 MHz
• Cpu: 8051-12C
• Max I/o Pins: 34
• Spi: 1
• Uart: 2
• Sram (kbytes): 8.25
• Self Program Memory: API
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 4
• Isp: UART/OCD
• Watchdog: Yes

Programmable
Clock-Output
78
AT89C51RE2
Figure 28. 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 29). The input clock increments TL2 at frequency F
counts to overflow from a loaded value. At overflow, the contents of RCAP2H and RCAP2L reg-
isters 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
(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 simultaneously. For
this configuration, the baud rates and clock frequencies are not independent since both func-
tions use the values in the RCAP2H and RCAP2L registers.
Clock O
CLK PERIPH
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.
– 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
FFh
1
)
CLK PERIPH
T2CON
TR2
/2.The timer repeatedly
T2EX:
if DCEN=1, 1=UP
if DCEN=1, 0=DOWN
if DCEN = 0, up counting
T2CON
TOGGLE
TF2
7663E–8051–10/08
T2CON
EXF2
INTERRUPT
TIMER 2