AT89LP51 datasheet(52/113 Pages) ATMEL

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3709C–MICRO–5/11

AT89LP51/52 - Preliminary

12.1

Timer 2 Registers

Control and status bits for Timer 2 are contained in registers T2CON (see Table 12-3) and

T2MOD (see Table 12-4). The register pair {TH2, TL2} at addresses 0CDH and 0CCH are the

16-bit timer register for Timer 2. The register pair {RCAP2H, RCAP2L} at addresses 0CBH and

0CAH are the 16-bit Capture/Reload register for Timer 2 in capture and auto-reload modes.

Table 12-3.

T2CON – Timer/Counter 2 Control Register

T2CON Address = 0C8H

Reset Value = 0000 0000B

Bit Addressable

TF2

EXF2

RCLK

TCLK

EXEN2

TR2

C/T2

CP/RL2

Bit

654

321

Symbol

Function

TF2

Timer 2 overflow flag set by a Timer 2 overflow and must be cleared by software. TF2 will not be set when either

RCLK = 1 or TCLK = 1.

EXF2

Timer 2 external flag set when either a capture or reload is caused by a negative transition on T2EX and EXEN2 = 1.

When Timer 2 interrupt is enabled, EXF2 = 1 will cause the CPU to vector to the Timer 2 interrupt routine. EXF2 must be

cleared by software. EXF2 does not cause an interrupt in up/down counter mode (DCEN = 1) or dual-slope mode.

RCLK

Receive clock enable. When set, causes the serial port to use Timer 2 overflow pulses for its receive clock in serial port

Modes 1 and 3. RCLK = 0 causes Timer 1 overflows to be used for the receive clock.

TCLK

Transmit clock enable. When set, causes the serial port to use Timer 2 overflow pulses for its transmit clock in serial port

Modes 1 and 3. TCLK = 0 causes Timer 1 overflows to be used for the transmit clock.

EXEN2

Timer 2 external enable. When set, allows a capture or reload to occur as a result of a negative transition on T2EX if

Timer 2 is not being used to clock the serial port. EXEN2 = 0 causes Timer 2 to ignore events at T2EX.

TR2

Start/Stop control for Timer 2. TR2 = 1 starts the timer.

C/T2

Timer or counter select for Timer 2. C/T2 = 0 for timer function. C/T2 = 1 for external event counter (falling edge

triggered).

CP/RL2

Capture/Reload select. CP/RL2 = 1 causes captures to occur on negative transitions at T2EX if EXEN2 = 1. CP/RL2 = 0

causes automatic reloads to occur when Timer 2 overflows or negative transitions occur at T2EX when EXEN2 = 1. When

either RCLK or TCLK = 1, this bit is ignored and the timer is forced to auto-reload on Timer 2 overflow.

Table 12-4.

T2MOD – Timer 2 Mode Control Register

T2MOD Address = 0C9H

Reset Value = 0000 0000B

Not Bit Addressable

–––

––

–

T2OE

DCEN

Bit

765

210

Symbol

Function

T2OE

Timer 2 Output Enable. When T2OE = 1 and C/T2 = 0, the T2 pin will toggle after every Timer 2 overflow.

DCEN

Timer 2 Down Count Enable. When Timer 2 operates in Auto-Reload mode and EXEN2 = 1, setting DCEN = 1 will cause

Timer 2 to count up or down depending on the state of T2EX.

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