Specifications

68
3706C–MICRO–2/11
AT89LP3240/6440
erator, T2EX can be used as an extra external interrupt. Also note that the Baud Rate and
Frequency Generator modes may be used simultaneously.
Figure 12-8. Timer 2 in Baud Rate Generator Mode
12.5 Frequency Generator (Programmable Clock Out)
Timer 2 ca n generate a 50% duty cycle clock on T2 (P1.0), as shown in Figure 12-9. This pin,
besides being a regular I/O pin, has two alternate functions. It can be programmed to input the
external clock for Timer/Counter 2 or to toggle its output at every timer overflow. To configure
the Timer/Counter 2 as a clock generator, bit C/T2
(T2CON.1) must be cleared and bit T2OE
(T2MOD.1) must be set. Bit TR2 (T2CON.2) starts and stops the timer.
The clock-out frequency depends on the oscillator frequency and the reload value of Timer 2
capture registers (RCAP2H, RCAP2L), as shown in the following equations.
In the frequency generator mode, Timer 2 roll-overs will not generate an interrupt. This behavior
is similar to when Timer 2 is used as a
baud-rate generator. It is possible to use Timer 2 as a
baud-rate generator and a clock generator simu ltaneously. Note, however, that the baud-rate
and clock-out frequencies cannot be determined independently from one another since they
both use RCAP2H and RCAP2L.
÷TPS
SMOD1
RCLK
TCLK
Rx
CLOCK
Tx
CLOCK
T2EX PIN
T2 PIN
TR2
"1"
"1"
"1"
"0"
"0"
"0"
TIMER 1 OVERFLOW
TIMER 2
INTERRUPT
2
16
16
RCAP2HRCAP2L
TL2 TH2
C/T2 = 0
C/T2 = 1
EXF2
TRANSITION
DETECTOR
EXEN2
÷
÷
÷
OSC
T2CM = 00B Clock Out Frequency
Oscillator Frequency
2 65536 RCAP2H,RCAP2L()–[]×
--------------------------------------------------------------------------------------------
1
TPS 1+
---------------------
×=
T2CM = 01B Clock Out Frequency
Oscillator Frequency
2 RCAP2H,RCAP2L()1+[]×
-------------------------------------------------------------------------------
1
TPS 1+
---------------------
×=