T89C51RD2-RDTIL datasheet(18/104 Pages) ATMEL

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T89C51RD2

4243G–8051–05/03

Timer 2

The timer 2 in the T89C51RD2 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 8) and

T2MOD register (See Table 9). 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, autoreload and Baud Rate Generator. These

modes are selected by the combination of RCLK, TCLK and CP/RL2 (T2CON), as

described in the ATMEL Wireless and Micrcontrollers 8-bit Microcontroller Hardware

description.

Refer to the ATMEL Wireless and Micrcontrollers 8-bit Microcontroller Hardware

description for the description of Capture and Baud Rate Generator Modes.

In T89C51RD2 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 Wireless and Micrcontrollers 8-bit Microcontroller Hardware description). If

DCEN bit is set, timer 2 acts as an Up/down timer/counter as shown in Figure 5. 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 the direc-

tion of the count. EXF2 does not generate any interrupt. This bit can be used to provide

17-bit resolution.

T89C51RD2-RDTIL Datasheet(PDF) 18 Page - ATMEL Corporation