AT89LP428 Atmel Corporation, AT89LP428 Datasheet - Page 57

• 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

12.3.2
3654A–MICRO–8/09
Up or Down Counter
Figure 12-3. Timer 2 Waveform: Auto-reload Mode (DCEN = 0)
Setting DCEN = 1 enables Timer 2 to count up or down, as shown in
the T2EX pin controls the direction of the count (if EXEN2 = 1). A logic 1 at T2EX makes Timer 2
count up. When T2CM
also causes BOTTOM, the 16-bit value in RCAP2H and RCAP2L, to be reloaded into the timer
registers, TH2 and TL2, respectively. A logic 0 at T2EX makes Timer 2 count down. The timer
underflows when TH2 and TL2 equal BOTTOM, the 16-bit value stored in RCAP2H and
RCAP2L. The underflow sets the TF2 bit and causes MAX to be reloaded into the timer regis-
ters. The EXF2 bit toggles whenever Timer 2 overflows or underflows and can be used as a 17th
bit of resolution. In this operating mode, EXF2 does not flag an interrupt.
When T2EX = 1 and T2CM
overflow also causes MIN to be reloaded into the timer registers. A logic 0 at T2EX makes Timer
2 count down. The timer underflows when TH2 and TL2 equal MIN. The underflow sets the TF2
bit and causes TOP to be reloaded into the timer registers. The behavior of Count Mode 0 ver-
sus Count Mode 0 when DCEN is enabled is shown in
mode.
Figure 12-4. Timer 2 Diagram: Auto-reload Mode (T2CM
Bottom
Max
Max
Top
Min
Min
÷TPS
1-0
= 00B, the timer will overflow at MAX and set the TF2 bit. This overflow
1-0
= 01B, the timer will overflow at TOP and set the TF2 bit. This
(Down Counting Reload Value)
(Up Counting Reload Value)
T2CM
T2CM
1-0
1-0
= 00B, DCEN = 0
= 01B, DCEN = 0
Overflow
Figure
1-0
= 00B, DCEN = 1)
12-5. EXF2 is not toggle in this
AT89LP428/828
Count
Direction
1 = Up
0 = Down
Figure
Toggle
12-4. In this mode,
Interrupt
Timer 2
TF2 Set
TF2 Set
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