TS80C51RA2 Atmel Corporation, TS80C51RA2 Datasheet - Page 18

• Manufacturer Part Number: TS80C51RA2
• Description: High Performance 8-bit Microcontroller
• Manufacturer: Atmel Corporation

Figure 5. Auto-reload Mode Up/Down Counter (DCEN = 1)
Programmable Clock-Output
18
TS8xC51Rx2
XTAL1
F
XTAL
In the clock-out mode, timer 2 operates as a 50%-duty-cycle, programmable clock gen-
erator (See Figure 6) . 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 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
Timer 2 is programmed for the clock-out mode as follows:
•
•
•
•
•
OSC
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.
/2
16)
to 4 MHz (F
Clock OutFrequency
F
OSC
(DOWN COUNTING RELOAD VALUE)
–
OSC
(:6 in X2 mode)
(UP COUNTING RELOAD VALUE)
/4). The generated clock signal is brought out to T2 pin (P1.0).
RCAP2L
T2
(8-bit)
:12
(8-bit)
(8-bit)
TL2
FFh
T2CONreg
RCAP2H
C/T2
(8-bit)
(8-bit)
=
TH2
(8-bit)
0
FFh
1
------------------------------------------------------------------------------------------- -
4
×
(
65536 RCAP2H
T2CONreg
TR2
–
T2EX:
if DCEN=1, 1=UP
if DCEN=1, 0=DOWN
if DCEN = 0, up
counting
F
TOGGLE
osc
T2CONreg
TF2
⁄
RCAP2L
T2CONreg
EXF2
INTERRUPT
TIMER 2
OSC
4188A–8051–10/02
/2. The timer
)