AT89LP428 Atmel Corporation, AT89LP428 Datasheet - Page 60

• Manufacturer Part Number: AT89LP428
• Manufacturer: Atmel Corporation

Specifications of AT89LP428

• Flash (kbytes): 4 Kbytes
• Max. Operating Frequency: 25 MHz
• Cpu: 8051-1C
• Max I/o Pins: 30
• Spi: 1
• Uart: 1
• Sram (kbytes): 0.75
• Eeprom (bytes): 512
• Self Program Memory: IAP
• Operating Voltage (vcc): 2.4 to 5.5
• Timers: 3
• Isp: SPI/OCD
• Watchdog: Yes

12.5
60
Frequency Generator (Programmable Clock Out)
AT89LP428/828
Timer 2 as a baud rate generator is shown in
TCLK = 1 in T2CON. Note that a rollover in TH2 does not set TF2 and will not generate an inter-
rupt. Note too, that if EXEN2 is set, a 1-to-0 transition in T2EX will set EXF2 but will not cause a
reload from (RCAP2H, RCAP2L) to (TH2, TL2). Thus when Timer 2 is in use as a baud rate
generator, T2EX can be used as an extra external interrupt. Also note that the Baud Rate and
Frequency Generator modes may be used simultaneously.
Figure 12-7. Timer 2 in Baud Rate Generator Mode
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 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 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.
T2EX PIN
OSC
T2 PIN
T2CM = 00B
T2CM = 01B
÷TPS
Transition
Detector
C/T2 = 0
C/T2 = 1
Clock Out Frequency
Clock Out Frequency
EXEN2
TR2
=
=
------------------------------------------------------------------------------------------- -
2
------------------------------------------------------------------------------ -
2
Figure
RCAP2L
×
TL2
×
[
[
65536
Oscillator Frequency
(
EXF2
RCAP2H,RCAP2L
Oscillator Frequency
12-7. This figure is valid only if RCLK or
RCAP2H
TH2
–
(
RCAP2H,RCAP2L
Interrupt
Timer 2
÷
2
)
"1"
"1"
+
1
Timer 1 Overflow
]
Figure
×
"0"
"0"
"0"
)
-------------------- -
TPS
]
×
1
"1"
-------------------- -
TPS
3654A–MICRO–8/09
+
12-8. This pin,
1
÷
SMOD1
RCLK
TCLK
÷
1
16
16
+
1
Clock
Clock
Rx
Tx