AT89S8252(2000) View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT89S8252
(Rev.:2000)

8-bit Microcontroller with 8K Bytes Flash

Atmel Corporation 

the transition was detected. Since two machine cycles (24

oscillator periods) are required to recognize a 1-to-0 transi-

tion, the maximum count rate is 1/24 of the oscillator

frequency. To ensure that a given level is sampled at least

once before it changes, the level should be held for at least

one full machine cycle.

Table 8. Timer 2 Operating Modes

RCLK + TCLK CP/RL2 TR2 MODE

0

0

1 16-bit Auto-reload

0

1

1 16-bit Capture

1

X

1 Baud Rate Generator

X

X

0 (Off)

Capture Mode

In the capture mode, two options are selected by bit

EXEN2 in T2CON. If EXEN2 = 0, Timer 2 is a 16 bit timer

or counter which upon overflow sets bit TF2 in T2CON.

This bit can then be used to generate an interrupt. If

EXEN2 = 1, Timer 2 performs the same operation, but a l-

to-0 transition at external input T2EX also causes the cur-

rent value in TH2 and TL2 to be captured into RCAP2H and

RCAP2L, respectively. In addition, the transition at T2EX

causes bit EXF2 in T2CON to be set. The EXF2 bit, like

TF2, can generate an interrupt. The capture mode is illus-

trated in Figure 1.

Figure 1. Timer 2 in Capture Mode

OSC

T2 PIN

T2EX PIN

÷12

C/T2 = 0

C/T2 = 1

TRANSITION

DETECTOR

CONTROL

TR2

CAPTURE

CONTROL

EXEN2

TH2

TL2

TF2

OVERFLOW

RCAP2H RCAP2L

EXF2

TIMER 2

INTERRUPT

10

AT89S8252

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