AT89C51CC02CA-TDSUM ATMEL [ATMEL Corporation], AT89C51CC02CA-TDSUM Datasheet - Page 65

• Manufacturer Part Number: AT89C51CC02CA-TDSUM
• Description: Enhanced 8-bit Microcontroller with CAN Controller and Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Programmable Clock-
Output
Figure 30. Clock-Out Mode
4126J–CAN–05/06
T2EX
CLOCK
T2
FT2
In clock-out mode, Timer 2 operates as a 50%-duty-cycle, programmable clock genera-
tor (Figure 30). 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.
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
C l o c k O u t F r e q u e n c y
/2
16)
Q
Q
Toggle
to 4 MHz (f
–
T2CON reg
D
EXEN2
T2CON.2
TR2
OSC
/4). The generated clock signal is brought out to T2 pin
=
T2CON reg
RCAP2L
EXF2
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
4
(8-bit)
(8-bit)
TL2
×
T2MOD reg
(
65536
T2OE
RCAP2H
(8-bit)
(8-bit)
TH2
–
F T
R C A P
2
INTERRUPT
TIMER 2
c l o c k
AT/T89C51CC02
OVERFLOW
2
H
⁄
R C A P
OSC
2
L
)
/2. The timer
65