AT80C51RA2-SLSUM データシートの表示（PDF） - Atmel Corporation

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AT80C51RA2-SLSUM

High Performance 8-bit Microcontrollers

Atmel Corporation 

AT/TS8xC51Rx2

6.2 Timer 2

The timer 2 in the TS80C51RX2 is compatible with the timer 2 in the 80C52.

It is a 16-bit timer/counter: the count is maintained by two eight-bit timer registers, TH2 and TL2,

connected in cascade. It is controlled by T2CON register (See Table 6-2) and T2MOD register

(See Table 6-3). 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 be incremented 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), as described in the

Atmel 8-bit Microcontroller Hardware description.

Refer to the Atmel 8-bit Microcontroller Hardware description for the description of Capture and

Baud Rate Generator Modes.

In TS80C51RX2 Timer 2 includes the following enhancements:

• Auto-reload mode with up or down counter

• Programmable clock-output

6.2.1

Auto-reload Mode

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 8-bit

Microcontroller Hardware description). If DCEN bit is set, timer 2 acts as an Up/down

timer/counter as shown in Figure 6-2. 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 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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4188F–8051–01/08

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