problem with 16X2 LCD

[chandrasekhar]

PLEASE ANY ONE HELP HOW TO MAKE DATA PINS(D7-D14) OF LCD TO HIGH.

i use pull up resistor(connected to vcc) for making these pins high but these pins are shoeing the voltage levels as ov.

where the problem is 

[chandrasekhar]

i have another problem with downloading the code in to mc through serial port

 

when switch on the power supply.then terminal shows the o/p all the 4 cases i.e

1.db9 connector 2&3 pins short

2.max-232 13 &14 pins short.

3.max-232 11&12 pins short.

4.microcontroller 10&11 pins short.

 

but when i tried to download the code in to the mc.

 

it is showing reset the device in to isp mode now .

 

even though after pressing the reset switch also.

please anyone help where is the problem

[chandrasekhar]

 

only lcd 12th pin is showing voltage level high and remaining data pins are showing low.

the pull up resistor(8 pins) connected to these data lines is showing low and pull up resistor 9th pin which is connected to vcc is high.

we used 3 pull up resistors 

1.at port 1 used for 7 switches (here all the 9 pins of pull up resistor is showing high)

2.at port2 used for data pins of lcd(only 9thpin showing high remaining pins is showing low)

3.at port 0 used for control pins (here all the 9 pins of pull up resistor is showing high)

please any one help where is the problem

[srihari.neppali]

when u initialise port as output port internal pullup are activated. if ur connecting data pins to P0 externall pullup n/w needed. 

[AJISH ALFRED]

Hi Chandrashekar,

It happen because your port pins has a default value (reset value). I assume that you are simply setting the pin as output and nothing else. Have you ever wondered what will be the value or voltage at that output pin, there should be some voltage no??

Go through your controller datasheet, that default value will be zero.

If the pin is generating zero voltage, it can never show high when you measure!!

[chandrasekhar]

my mc is 89v51RD2.PORT2 (21-28) IS BIDIRECTIONAL I/O PORT WITH INTERNAL PULLUP’S.

MY PULL UP RESISTOR SPECIFICATION IS A103J.

[AJISH ALFRED]

Hi,

No need to change the port. You should keep in mind that, there will be always a value at the port pins, either logic0 or logic1. Normally logic0 .i.e. 0V will be default.

If the pin produces logic0, then even if you pull up, the data lines will show 0volts only.

 

Simply set the pins as output and write a 1 (logic1) to those pins.

[AJISH ALFRED]

Learn more about pull up and pull down from the discussions in our forum

 

http://www.engineersgarage.com/forums/8051/pull-resistor 

http://www.engineersgarage.com/forums/electronics/pull-up-and-pull-down-resistors 

 

[chandrasekhar]

thank you sir.

so i need to change in code is it right

[chandrasekhar]

thank you sir

iam using port2 for lcd data pins.where i have to change these port pin values

[AJISH ALFRED]

Ya, I think so.

[Author]

Posts