T89C5115 ATMEL Corporation, T89C5115 Datasheet - Page 58

• Manufacturer Part Number: T89C5115
• Description: Low Pin Count 8-bit MCU with A/D Converter and 16-Kbytes of Flash Memory
• Manufacturer: ATMEL Corporation

Programmable Clock-
Output
Figure 28. Clock-out Mode
58
T89C5115
CLOCK
FT2
T2EX
T2
In clock-out mode, Timer 2 operates as a 50%-duty-cycle, programmable clock genera-
tor (See Figure 28). 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
pin (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.
T2CON reg
C/T2
OSC
1
0
Clock OutFrequency
/2
16)
–
to 4 MHz (F
T2CON.1
CT/2
0
1
T2CON reg
OSC
EXEN2
:2
/4). The generated clock signal is brought out to T2
T2CON.2
=
TR2
------------------------------------------------------------------------------------------- -
4
×
(
65536 RCAP2H
T2CON reg
EXF2
RCAP2L
–
(8-bit)
(8-bit)
FT2clock
TL2
T2MOD reg
T2OE
RCAP2H
(8-bit)
(8-bit)
TH2
⁄
RCAP2L
INTERRUPT
Timer 2
OVERFLOW
OSC
)
4128A–8051–04/02
/2. The timer