T89C51CC01 Atmel, T89C51CC01 Datasheet - Page 71

• Manufacturer Part Number: T89C51CC01
• Description: Enhanced 8-Bit Microcontroller
• Manufacturer: Atmel

Programmable Clock-
Output
Figure 37. Clock-Out Mode
4129K–CAN–01/05
T2EX
CLOCK
T2
FT2
In clock-out mode, timer 2 operates as a 50%-duty-cycle, programmable clock genera-
tor (See Figure 37). The input clock increments TL2 at frequency F
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 (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 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 OutFrequency
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.
OSC
–
/2
16)
to 4 MHz (F
Q
Q
Toggle
T2CON reg
D
EXEN2
=
T2CON.2
---------------------------------------------------------------------------------------- -
4
OSC
TR2
×
(
/4). The generated clock signal is brought out to T2 pin
65536 RCAP2H
–
T2CON reg
FT2clock
EXF2
RCAP2L
(8-bit)
(8-bit)
TL2
T2MOD reg
T2OE
RCAP2H
(8-bit)
⁄
(8-bit)
TH2
RCAP2L
INTERRUPT
TIMER 2
OVERFLOW
)
T89C51CC01
OSC
/2. The timer
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