AT89C51RE2 Atmel Corporation, AT89C51RE2 Datasheet - Page 77

• Manufacturer Part Number: AT89C51RE2
• Manufacturer: Atmel Corporation

Specifications of AT89C51RE2

• Flash (kbytes): 128 Kbytes
• Max. Operating Frequency: 60 MHz
• Cpu: 8051-12C
• Max I/o Pins: 34
• Spi: 1
• Uart: 2
• Sram (kbytes): 8.25
• Self Program Memory: API
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 4
• Isp: UART/OCD
• Watchdog: Yes

Timer 2
Auto-Reload Mode
7663E–8051–10/08
The Timer 2 in the AT89C51RE2 is the standard C52 Timer 2.
It is a 16-bit timer/counter: the count is maintained by two eight-bit timer registers, TH2 and TL2
are cascaded. It is controlled by T2CON (Table 52) and T2MOD (Table 53) registers. Timer 2
operation is similar to Timer 0 and Timer 1.C/T2 selects F
T2 (counter operation) as the timer clock input. Setting TR2 allows TL2 to increment by the
selected input.
Timer 2 has 3 operating modes: capture, autoreload and Baud Rate Generator. These modes
are selected by the combination of RCLK, TCLK and CP/RL2 (T2CON).
Refer to the Atmel 8-bit Microcontroller Hardware description for the description of Capture and
Baud Rate Generator Modes.
Timer 2 includes the following enhancements:
•
•
The auto-reload mode configures Timer 2 as a 16-bit timer or event counter with automatic
reload. If DCEN bit in T2MOD is cleared, Timer 2 behaves as in 80C52 (refer to the Atmel C51
Microcontroller Hardware description). If DCEN bit is set, Timer 2 acts as an Up/down
timer/counter as shown in Figure 28. In this mode the T2EX pin controls the direction of count.
When T2EX is high, Timer 2 counts up. Timer overflow occurs at FFFFh which sets the TF2 flag
and generates an interrupt request. The overflow also causes the 16-bit value in RCAP2H and
RCAP2L registers to be loaded into the timer registers TH2 and TL2.
When T2EX is low, Timer 2 counts down. Timer underflow occurs when the count in the timer
registers TH2 and TL2 equals the value stored in RCAP2H and RCAP2L registers. The under-
flow sets TF2 flag and reloads FFFFh into the timer registers.
The EXF2 bit toggles when Timer 2 overflows or underflows according to the direction of the
count. EXF2 does not generate any interrupt. This bit can be used to provide 17-bit resolution.
Auto-reload mode with up or down counter
Programmable clock-output
OSC
/12 (timer operation) or external pin
AT89C51RE2
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