13
0811E–MICRO–9/08
AT89LV55
Figure 9-1.
Timer 2 in Clock-out Mode
10. Programmable Clock Out
A 50% duty cycle clock can be programmed to come out on P1.0, as shown in
Figure 9-1. 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 output a 50% duty cycle clock ranging from 61 Hz to
3 MHz at a 12 MHz operating frequency.
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, TCAP2L), as shown in the following equation:
In the clock-out 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 gen-
erator and a clock generator simultaneously. Note, however, that the baud-rate and clock-out
frequencies cannot be determined independently from one another since they both use
RCAP2H and RCAP2L.
11. UART
The UART in the AT89LV55 operates the same way as the UART in the AT89C51. For further
information on the UART operation, please click on the document link below:
http://www.atmel.com/dyn/resources/prod_documents/DOC4316.PDF
Clock-Out Frequency
Oscillator Frequency
4
65536
RCAP2H RCAP2L
(,
)
–
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