AT80C51RB2-SLSIM datasheet(17/83 Pages) ATMEL

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AT80C51RD2/AT83C51Rx2

4113B–8051–03/05

Timer 2

The Timer 2 in the T8xc51Rx2 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 9) and T2MOD (Table 10) reg-

isters. Timer 2 operation is similar to Timer 0 and Timer 1. C/T2 selects F

OSC/12 (timer

operation) or external pin T2 (counter operation) as the timer clock input. Setting TR2

allows TL2 to be incremented by the selected input.

Timer 2 has 3 operating modes: capture, auto-reload 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 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 8-bit Microcontroller Hardware description). If DCEN bit is set, Timer 2 acts

as an Up/down timer/counter as shown in Figure 6. 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.

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