Programmable Clock Output - Atmel AT89C5131A-L Manual

Figure 26. Auto-reload Mode Up/Down Counter (DCEN = 1)
F
CLK PERIPH
Programmable Clock
Output
4338F–USB–08/07
: 6
(DOWN COUNTING RELOAD VALUE)
RCAP2L
(UP COUNTING RELOAD VALUE)
In the Clock-out mode, Timer 2 operates as a 50%-duty-cycle, programmable clock gen-
erator (See Figure 27). The input clock increments TL2 at frequency F
timer 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 following formula gives the Clock-out fre-
quency as a function of the system oscillator frequency and the value in the RCAP2H
and RCAP2L registers
Clock OutFrequency –
For a 16 MHz system clock, Timer 2 has a programmable frequency range of 61 Hz
16)
(F /2 to 4 MHz (F
CLK PERIPH
T2 pin (P1.0).
Timer 2 is programmed for the Clock-out mode as follows:
• 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.
0
1
T2
TR2
C/T2
T2CON
T2CON
FFh FFh
(8-bit) (8-bit)
TL2 TH2
(8-bit) (8-bit)
RCAP2H
(8-bit) (8-bit)
---------------------------------------------------------------------------------------- -
=
4 65536 RCAP2H
× (
/4). The generated clock signal is brought out to
CLK PERIPH
AT89C5131A-L
T2EX:
if DCEN = 1, 1 = UP
if DCEN = 1, 0 = DOWN
if DCEN = 0, up counting
T2CON
TOGGLE
EXF2
Timer 2
TF2
INTERRUPT
T2CON
CLK PERIPH
F
CLKPERIPH
– ⁄ RCAP2L )
/2. The
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