STC89LE52RC datasheet(103/165 Pages) STC

103 / 165 page

The Timer 2 as a baud rate generator mode is valid only if RCLK and/or TCLK=1 in T2CON register. Note that

a rollover in TH2 does not set TF2, and will not generate an interrupt. Thus, the Timer 2 interrupt does not have

to be disabled when Timer 2 is in the baud rate generator mode. Also if the EXEN2 (T2 external enable bit) is set,

a 1-to-0 transition in T2EX (Timer/counter 2 trigger input) will set EXF2 (T2 external flag) but will not cause

a reload from (RCAP2H, RCAP2L) to (TH2,TL2). Therefore when Timer 2 is in use as a baud rate generator,

T2EX can be used as an additional external interrupt, if needed.

It should be noted that when Timer 2 is running (TR2=1) in "timer" function in the baud rate generator mode, one

should not try to read or write TH2 and TL2. As a baud rate generator, Timer 2 is incremented at 1/2 the system

clock or asynchronously from pin T2; under these conditions, a read or write of TH2 or TL2 may not be accurate.

The RCAP2 registers may be read, but should not be written to, because a write might overlap a reload and cause

write and/or reload errors. The timer should be turned off (clear TR2) before accessing the Timer 2 or RCAP2

registers.

Timer 2

Interrupt

SYSclk

÷2

control

C/T2=0

C/T2=1

T2 Pin

T2EX Pin

MCU in 12T mode

MCU in 6T mode

TL2

(8 Bits)

RCAP2L

Timer 2 in Baud-Rate Generator Mode

÷12

÷6

TR2

TH2

(8 Bits)

RCAP2H

EXF2

Transition

Detector

control

EXEN2

'0' '1'

'1'

'0'

÷16

'1'

'0'

Timer 1

Overflow

SMOD

RCLK

RX Clock

TX Clock

TCLK

Reload

The following program is an assembly language code that domestrates Timer 2 of STC89xx series MCU acted as

baud rate generator.

;/*------------------------------------------------------------------------------------------------------------*/

;/* --- STC MCU International Limited ----------------------------------------------------------------*/

;/* --- STC 89xx Series MCU Timer 2 as Baud Rate Generoter Demo ------------------------*/

;/* If you want to use the program or the program referenced in the */

;/* article, please specify in which data and procedures from STC */

;/*--------------------------------------------------------------------------------------------------------------*/

;Declare STC89xx series MCU SFRs

;SFRs associated with Timer 2 and RS232 port

T2CON

EQU

0C8H

TR2

EQU

T2CON.2

;TR2 is the second bit in SFR—T2CON

103

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