AT83C5103 datasheet(29/64 Pages) ATMEL

29 / 64 page

AT8xC5103

4134C–8051–09/04

Mode 3 (Two 8-bit Timers)

Mode 3 configures Timer 0 such that registers TL0 and TH0 operate as separate 8-bit

Timers (see Figure 18). This mode is provided for applications requiring an additional 8-

bit Timer or Counter. TL0 uses the Timer 0 control bits C/T0# and GATE0 in TMOD reg-

ister, and TR0 and TF0 in TCON register in the normal manner. TH0 is locked into a

Timer function (counting FPER /6) and takes over use of the Timer 1 interrupt (TF1) and

run control (TR1) bits. Thus, operation of Timer 1 is restricted when Timer 0 is in Mode

Figure 18. Timer/Counter 0 in Mode 3: Two 8-bit Counters

Timer 1

Timer 1 is identical to Timer 0 excepted 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 15 through Figure 17 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 15)

and bits 2, 3, 6 and 7 of TCON register (see Figure 14). 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 Timer/Counter before changing mode.

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

PERIPH

CLOCK

÷ 6

PERIPH

CLOCK

÷ 6

AT83C5103 Datasheet(PDF) 29 Page - ATMEL Corporation

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