AT89LP51 Atmel Corporation, AT89LP51 Datasheet - Page 56

• Manufacturer Part Number: AT89LP51
• Manufacturer: Atmel Corporation

Specifications of AT89LP51

• Flash (kbytes): 4 Kbytes
• Max. Operating Frequency: 20 MHz
• Cpu: 8051-1C
• Max I/o Pins: 36
• Uart: 1
• Sram (kbytes): 0.25
• Eeprom (bytes): 256
• Self Program Memory: IAP
• Operating Voltage (vcc): 2.4 to 5.5
• Timers: 3
• Isp: SPI
• Watchdog: Yes

Figure 12-6. Timer 2 in Baud Rate Generator Mode
12.5
Figure 12-7. Timer 2 in Clock-out Mode
56
Frequency Generator (Programmable Clock Out)
AT89LP51/52
T2EX PI N
OSC
T2 PI N
T2EX PIN
T2 PIN
Timer 2 can generate a 50% duty cycle clock on T2 (P1.0), as shown in
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 system frequency and the reload value of Timer 2 capture registers (RCAP2H,
RCAP2L), as shown in the following equation.
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 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.
÷CDV
OSC
TRANSITION
DETECT OR
C/T2 = 0
C/T2 = 1
÷CDV
TRANSITION
DETECTOR
Clock Out Frequency
EXEN2
TR2
C/T2
EXEN2
TR2
RCAP2L
TL2
EXF2
=
RCAP2H
------------------------------------------------------------------------------------------- -
2
TH2
×
RCAP2L
TL2
[
÷2
65536
EXF2
System Frequency
INTERR UPT
TIMER 2
RCAP2H
–
÷
TH2
(
2
RCAP2H,RCAP2L
"1"
"1"
TIMER 1 OVERFLOW
"0"
"0"
"0"
T2OE
INTERRUPT
TIMER 2
"1"
÷
SMOD1
RCLK
TCLK
÷
16
16
)
]
Figure
CLOCK
CLOCK
Rx
Tx
3709D–MICRO–12/11
13.. This pin,