AT89LP51 Atmel Corporation, AT89LP51 Datasheet - Page 54

• 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 12-2. Timer 2 Diagram: Auto-Reload Mode (DCEN = 0)
Figure 12-3. Timer 2 Waveform: Auto-Reload Mode (DCEN = 0)
12.3.2
Figure 12-4. Timer 2 Waveform: Auto-Reload Mode (DCEN = 1)
54
AT89LP51/52
Up or Down Counter
OSC
BOTTOM
BOTTOM
÷CDV
T2EX
EXF2
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.
The behavior of Timer 2 when DCEN is enabled is shown in
MAX
MAX
MIN
MIN
÷TPS
1-0
= 00B, the timer will overflow at MAX and set the TF2 bit. This overflow
TL2
TH2
Figure
TF2 Set
TF2 Set
12-4.
Figure
12-5. In this mode,
3709D–MICRO–12/11