AT80SND1C-ROTIL datasheet(54/210 Pages) ATMEL

54 / 210 page

AT8xC51SND1C

4109E–8051–06/03

3. Figure 34 gives the autoreload period calculation formulas for both TF0 and TF1

flags.

Figure 35. Timer/Counter 0 in Mode 3: 2 8-bit Counters

Figure 36. Mode 3 Overflow Period Formula

Timer 1

Timer 1 is identical to Timer 0 except for Mode 3 which is a hold-count mode. The fol-

lowing comments help to understand the differences:

•

Timer 1 functions as either a Timer or event Counter in three modes of operation.

Figure 29 through Figure 33 show the logical configuration for modes 0, 1, and 2.

Timer 1’s mode 3 is a hold-count mode.

•

Timer 1 is controlled by the four high-order bits of TMOD register (see Figure 61)

and bits 2, 3, 6 and 7 of TCON register (see Figure 60). TMOD register selects the

method of Timer gating (GATE1), Timer or Counter operation (C/T1#) and mode of

operation (M11 and M01). TCON register provides Timer 1 control functions:

overflow flag (TF1), run control bit (TR1), interrupt flag (IE1) and interrupt type

control bit (IT1).

•

Timer 1 can serve as the Baud Rate Generator for the Serial Port. Mode 2 is best

suited for this purpose.

•

For normal Timer operation (GATE1 = 0), setting TR1 allows TL1 to be incremented

by the selected input. Setting GATE1 and TR1 allows external pin INT1 to control

Timer operation.

•

Timer 1 overflow (count rolls over from all 1s to all 0s) sets the TF1 flag generating

an interrupt request.

•

When Timer 0 is in mode 3, it uses Timer 1’s overflow flag (TF1) and run control bit

(TR1). For this situation, use Timer 1 only for applications that do not require an

interrupt (such as a Baud Rate Generator for the Serial Port) and switch Timer 1 in

and out of mode 3 to turn it off and on.

•

It is important to stop the Timer/Counter before changing modes.

TR0

TCON.4

TF0

TCON.5

INT0

GATE0

TMOD.3

Overflow

Timer 0

Interrupt

Request

C/T0#

TMOD.2

TL0

(8 bits)

TR1

TCON.6

TH0

(8 bits)

TF1

TCON.7

Overflow

Timer 1

Interrupt

Request

TIM0

CLOCK

÷ 6

TIM0

CLOCK

÷ 6

TF0PER =

TIM0

⋅ (256 – TL0)

TF1

PER =

FTIM0

⋅ (256 – TH0)

AT80SND1C-ROTIL Datasheet(PDF) 54 Page - ATMEL Corporation

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