AT89LP51 datasheet(59/113 Pages) ATMEL

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3709B–MICRO–12/10

AT89LP51/52 - Preliminary

The Timer 1 overflow rate normally determines the baud rates in Modes 1 and 3. When Timer 1

is the baud rate generator, the baud rates are determined by the Timer 1 overflow rate and the

value of SMOD1 according to the following equation:

The Timer 1 interrupt should be disabled in this application. The Timer itself can be configured

for either timer or counter operation in any of its 3 running modes. In the most typical applica-

tions, it is configured for timer operation in auto-reload mode (high nibble of TMOD = 0010B). In

this case, the baud rate is given by the following formula:

Table 14-2 lists commonly used baud rates and how they can be obtained from Timer 1.

14.2.2

Using Timer 2 to Generate Baud Rates

Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in T2CON. Under

these conditions, the baud rates for transmit and receive can be simultaneously different by

using Timer 1 for transmit and Timer 2 for receive, or vice versa. The baud rate generator mode

Modes 1, 3

Baud Rate

SMOD1

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

(Timer 1 Overflow Rate)

Modes 1, 3

Baud Rate

SMOD1

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

System Frequency

256

TH1

()

–

[]

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

TPS

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

Table 14-2.

Commonly Used Baud Rates Generated by Timer 1

Baud Rate

fOSC (MHz)

CDV

SMOD1

Timer 1

C/T

Mode

TPS

Reload Value

Mode 0 Max: 6 MHz

Mode 2 Max: 750K

Modes 1, 3 Max: 750K

F4H

19.2K

11.059

DCH

9.6K

11.059

DCH

4.8K

11.059

B8H

2.4K

11.059

70H

1.2K

11.059

FEE0H

137.5

11.986

F55CH

110

F2AFH

110

F2AFH

19.2K

11.059

FDH

9.6K

11.059

FDH

4.8K

11.059

FAH

2.4K

11.059

F4H

1.2K

11.059

E8H

137.5

11.986

1DH

110

72H

110

FEEBH

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