AT89LP51 datasheet(46/113 Pages) ATMEL

46 / 113 page

3709B–MICRO–12/10

AT89LP51/52 - Preliminary

11.1

Mode 0 – 13-bit Timer/Counter

Both Timers in Mode 0 are 8-bit Counters with a divide-by-32 prescaler. Figure 11-1 shows the

Mode 0 operation as it applies to Timer 1. As the count rolls over from all “1”s to all “0”s, it sets

the Timer interrupt flag TF1. The counter input is enabled to the Timer when TR1 = 1 and either

GATE1 = 0 or INT1 =1. Setting GATE1 = 1 allows the Timer to be controlled by external input

INT1, to facilitate pulse width measurements. TR1 is a control bit in the Special Function Regis-

ter TCON. GATE1 is in TMOD. The 13-bit register consists of all 8 bits of TH1 and the lower 5

bits of TL1. The upper 3 bits of TL1 are indeterminate and should be ignored. Setting the run flag

(TR1) does not clear the registers.

Figure 11-1. Timer/Counter 1 Mode 0: 13-bit Counter

Mode 0 operation is the same for Timer 0 as for Timer 1, except that TR0, TF0, GATE0 and

INT0 replace the corresponding Timer 1 signals in Figure 11-1. There are two different C/T bits,

one for Timer 1 (TMOD.6) and one for Timer 0 (TMOD.2).

11.2

Mode 1 – 16-bit Timer/Counter

In Mode 1 the Timers are configured for 16-bit operation. The Timer register is run with all 16 bits

and the clock is applied to the combined high and low timer registers (TH1/TL1). As clock pulses

are received, the timer counts up: 0000H, 0001H, 0002H, etc. An overflow occurs on the

FFFFH-to-0000H transition, upon which the overflow flag bit in TCON is set. See Figure 11-2.

Mode 1 operation is the same for Timer/Counter 0.

Figure 11-2. Timer/Counter 1 Mode 1: 16-bit Counter

Mode 0:

Time-out Period

8192

System Frequency

--------------------------------------------------

TPS

()

OSC

T1 Pin

TR1

GATE1

INT1 Pin

TL1

(5 Bits)

Control

Interrupt

C/T = 0

C/T = 1

TH1

(8 Bits)

TF1

÷CDV

÷TPS

Mode 1:

Time-out Period

65536

System Frequency

--------------------------------------------------

TPS

()

OSC

T1 Pin

TR1

GATE1

INT1 Pin

TL1

(8 Bits)

Control

Interrupt

C/T = 0

C/T =1

TH1

(8 Bits)

TF1

÷CDV

÷TPS

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