AT89LP51 Atmel Corporation, AT89LP51 Datasheet - Page 51

• 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

12. Timer 2
3709D–MICRO–12/11
The AT89LP51/52 includes a 16-bit Timer/Counter 2 with the following features:
Timer 2 is a 16-bit Timer/Counter that can operate as either a timer or an event counter. The
type of operation is selected by bit C/T2 in the SFR T2CON. Timer 2 has three operating modes:
capture, auto-reload (up or down counting), and baud rate generator. The modes are selected
by bits in T2CON and T2MOD, as shown in
the Compare/Capture Array (See
Timer 2 consists of two 8-bit registers, TH2 and TL2. In the Timer function, the register is incre-
mented every clock cycle. Since a clock cycle consists of one oscillator period, the count rate is
equal to the oscillator frequency. The timer rate can be prescaled by a value between 1 and 16
using the Timer Prescaler (see
In the Counter function, the register is incremented in response to a 1-to-0 transition at its corre-
sponding external input pin, T2. In this function, the external input is sampled every clock cycle.
When the samples show a high in one cycle and a low in the next cycle, the count is incre-
mented. The new count value appears in the register during the cycle following the one in which
the transition was detected. Since two clock cycles are required to recognize a 1-to-0 transition,
the maximum count rate is 1/2 of the oscillator frequency. To ensure that a given level is sam-
pled at least once before it changes, the level should be held for at least one full clock cycle.
Table 12-1.
The following definitions for Timer 2 are used in the subsequent paragraphs:
Table 12-2.
RCLK + TCLK
• 16-bit timer/counter with one 16-bit reload/capture register
• One external reload/capture input
• Up/Down counting mode with external direction control
• UART baud rate generation
• Output-pin toggle on timer overflow
• Dual slope symmetric operating modes
• Timer 2 is included in AT89LP51, unlike AT89S51.
BOTTOM
Symbol
MAX
MIN
X
X
0
0
0
1
Timer 2 Operating Modes
Timer 2 Definitions
Definition
0000H
FFFFH
16-bit value of {RCAP2H,RCAP2L}
CP/RL2
X
X
X
0
0
1
DCEN
X
X
X
X
0
1
Table 6-2 on page
Section 13. “External Interrupts” on page
T2OE
X
X
0
0
0
1
Table
12-3. Timer 2 also serves as the time base for
TR2
31).
1
1
1
1
1
0
MODE
16-bit Auto-reload
16-bit Auto-reload Up-Down
16-bit Capture
Baud Rate Generator
Frequency Generator
(Off)
AT89LP51/52
57).
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