AT89LP51 datasheet(60/113 Pages) ATMEL

60 / 113 page

3709B–MICRO–12/10

AT89LP51/52 - Preliminary

is similar to the auto-reload mode, in that a rollover causes the Timer 2 registers to be reloaded

with the 16-bit value in registers RCAP2H and RCAP2L, which are preset by software. In this

case, the baud rates in Modes 1 and 3 are determined by Timer 2’s overflow rate according to

the following equation:

Table 14-3 lists commonly used baud rates and how they can be obtained from Timer 2.

14.3

Framing Error Detection

In addition to all of its usual modes, the UART can perform framing error detection by looking for

missing stop bits, and automatic address recognition. When used for framing error detect, the

UART looks for missing stop bits in the communication. A missing bit will set the FE bit in the

SCON register. The FE bit shares the SCON.7 bit with SM0 and the function of SCON.7 is deter-

mined by PCON.6 (SMOD0). If SMOD0 is set then SCON.7 functions as FE. SCON.7 functions

as SM0 when SMOD0 is cleared. When used as FE, SCON.7 can only be cleared by software.

The FE bit will be set by a framing error regardless of the state of SMOD0.

14.4

Automatic Address Recognition

Automatic Address Recognition is a feature which allows the UART to recognize certain

addresses in the serial bit stream by using hardware to make the comparisons. This feature

saves a great deal of software overhead by eliminating the need for the software to examine

every serial address which passes by the serial port. This feature is enabled by setting the SM2

bit in SCON for Modes 1, 2 or 3. In the 9-bit UART modes, Mode 2 and Mode 3, the Receive

Table 14-3.

Commonly Used Baud Rates Generated by Timer 2

Baud Rate

OSC (MHz)

CDV

Timer 2

CP/RL2

C/T2

TCLK or RCLK

Reload Value

Max: 750K

FFFFH

19.2K

11.059

FFDCH

9.6K

11.059

FFB8H

4.8K

11.059

FF70H

2.4K

11.059

FEE0H

1.2K

11.059

FDC0H

137.5

11.9860

EAB8H

110

F2AFH

110

E55EH

19.2K

11.059

FFEEH

9.6K

11.059

FFDCH

4.8K

11.059

FFB8H

2.4K

11.059

FF70H

1.2K

11.059

FEE0H

137.5

11.986

F55CH

110

F2AFH

Modes 1 and 3

Baud Rate

------

System Frequency

65536

RCAP2H,RCAP2L

()

–

[]

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