at89c51ac3-s3sim ATMEL Corporation, at89c51ac3-s3sim Datasheet - Page 75

• Manufacturer Part Number: at89c51ac3-s3sim
• Description: At89c51ac3 Enhanced 8-bit Microcontroller With 64kb Flash Memory
• Manufacturer: ATMEL Corporation

Programmable Clock-
Output
Figure 41. Clock-Out Mode
4383D–8051–02/08
T2EX
CLOCK
T2
FT2
In clock-out mode, timer 2 operates as a 50%-duty-cycle, programmable clock genera-
tor (See Figure 41). 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
Clock OutFrequency
/2
16)
–
to 4 MHz (F
Q
Q
Toggle
T2CON reg
D
EXEN2
T2CON.2
OSC
TR2
/4). The generated clock signal is brought out to T2 pin
=
---------------------------------------------------------------------------------------- -
4
×
(
T2CON reg
65536 RCAP2H
EXF2
RCAP2L
(8-bit)
(8-bit)
TL2
T2MOD reg
T2OE
–
FT2clock
RCAP2H
(8-bit)
(8-bit)
TH2
INTERRUPT
TIMER 2
⁄
RCAP2L
OVERFLOW
)
OSC
/2. The timer
75