Problem with 7805 and 89c51 for transferring data serially to PC

• Nov 7, 2006

• #1

M

mnoman

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I am using 7805 with the 89c51 to transfer data serially to PC the problem is that while the power is ON no data is displayed on the PC as soon as the I switch of the power a burst of DATA is displayed OR if the switch is made to ON and OFF several times then it becomes OK and start sending data continiously. I think that it is the problem with 7805 as I had connected Two 7805 with the single supply one for 89c51 and other for some other circuits
can any one know how to solve the problem.

 

• Nov 7, 2006

• #2

E

echo47

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problem with 7805

When you see no data on the PC, is the 89C51 outputting anything at all, or is it dead? Check with an oscilloscope.

If it is sending data but nothing appears on the PC, what software is displaying the data? Maybe the data is corrupt, so the PC software displays nothing. Try viewing the data with a dumb-terminal utility such as Windows Hyper Terminal. Also try plugging and unplugging the serial cable a few times to see if the data suddenly starts working. That would be caused by what I call "false start bit syndrome".

 

• Nov 8, 2006

• #3

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IanP

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Re: problem with 7805

It is very unlikely your problem is related to the 7805 voltage regulator ..
If, as you said, occasionally you have correct string on the PC's screen, try this:
Connect a switch to the reset pin of the 89C51 (of course you should have a cap there) and +5V, turn the power on, wait a couple of seconds and manually reset the micro ..
What do you have now?

Regards,
IanP

 

• Nov 8, 2006

• #4

budhy

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Re: problem with 7805

Try this small program

Code:

     MOV   SMOD,#$53
     MOV   TMOD,#2
     MOV   TH0,#$FD        ; 9600 Baud
     SET   TR1
;
CharOut:
     JNB   TI,CharOut
     CLR   TI
     MOV   SBUF,#'A'
     SJMP  CharOut

if it can continously sent character 'A' to HyperTerminal, its mean your hardware configuration is OK, else recheck your program and/or HyperTerminal setup

 

• Nov 8, 2006

• #5

king_rero

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Re: problem with 7805

may be ur problem with hardware failer point acting like current sinker.!

 

• Nov 8, 2006

• #6

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mehdi_394

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problem with 7805

i have done this project (sending from8051 to pc)
do you convert the ttl voltage level of 8051 to rs232 voltage level?

this maybe ur problem.... I think

 

• Nov 8, 2006

• #7

S

sento

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Re: problem with 7805

serial port on PC have ±12V logic !!!

log1 ... H ... -12V ÷ -3V
log0 ... L ... +3V ÷ +12V

You must convert ±12V to TTL; Use ic MAX232 for voltage conversion.

 

• Nov 10, 2006

• #8

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adnan_wns

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problem with 7805

check ur programming
if its ok
then their must be problem in ur power supply

 

• Nov 29, 2006

• #9

J

jayavardhan

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Re: problem with 7805

may be ur problem with hardware

 

• Nov 29, 2006

• #10

R

rashslash

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Re: problem with 7805

use max232 with serial and controller

 

• Nov 30, 2006

• #11

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manish12

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Re: problem with 7805

Prob only with the reset + baudrate[may be your prog / xtal] + null modem connection.
thats it.

 

• Nov 30, 2006

• #12

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eng_ahmed22

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Re: problem with 7805

hi
i think it is a RESET Circuit problem
chek it
best luck
Ahmed

 

• Nov 30, 2006

• #13

qmriso

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Re: problem with 7805

i'm agree with ahmed...maybe because of the reset circuit...sometime i also face the same prob..

 

• Nov 30, 2006

• #14

Gladis

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Re: problem with 7805

Hi, Problem ia absolutly not with 7805, may be with ur code. Put a small delay for power-up approx:100ms at the beginning of the code. Which transformer are u using?