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Problem with 74LS244 or ????

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aspirantnew

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74ls244

Hi all

I have interfaced an 8255 chip to the ISA bus.I ve connected LEDs to all the three ports for testing.The connections are fine and program to switch on and off the LEDs are working perfectly.
The problem is that ,for safety purposes,i connected three 74LS244 chips to each of the ports of the 8255 and then tried to drive the LEDs.But unfortunately,as soon as i plug in the board to the ISA slot of my PC,all of these 24 LEDs glow,which obviuosly means all the outputs of the buffer chip 74LS244 are automatically getting HIGH.Can anyone help me with this, Please?

Without the 74LS244, the ports are working properly and we even have interfaced an ADC and it is working fine.

Please help.
 

IanP

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74hc244 versus 74ls244

If enable pins (1 and 19) are low the outputs of the 244 just follow the inputs, so you must have High on all 8255 pins ..

Regards,
IanP
 

yogi

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interfacing 74ls244 with 8051

this is due to the property of 74ls244 which takes high impedance state as HIGH. At the startup all ports of 8255 is configured as input port and this is taken as HIHG. That is the problem. Try with 74HC244. Why u need 244????. For more about these types of problems see my books for robotics, parallel port,avr microcontroller


you can get it from yahoo group-booksbybibin
http://groups.yahoo.com/group/booksbybibin/
 

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