AT89C51ED2-RDTIM datasheet(31/137 Pages) ATMEL

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AT89C51RD2/ED2

4235E–8051–04/04

Timer 2

The Timer 2 in the AT89C51RD2/ED2 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 20) and T2MOD (Table 21) registers. Timer

2 operation is similar to Timer 0 and Timer 1. C/T2 selects FOSC/12 (timer operation) or

external pin 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 Manual for the description of Capture

and Baud Rate Generator Modes.

Timer 2 includes the following enhancements:

•

Auto-reload mode with up or down counter

•

Programmable clock-output

Auto-reload Mode

The auto-reload mode configures Timer 2 as a 16-bit timer or event counter with auto-

matic reload. If DCEN bit in T2MOD is cleared, Timer 2 behaves as in 80C52 (refer to

the Atmel C51 Microcontroller Hardware Manual). If DCEN bit is set, Timer 2 acts as an

Up/down timer/counter as shown in Figure 14. 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 underflow 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.

AT89C51ED2-RDTIM 数据表(PDF) 31 Page - ATMEL Corporation