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PIC&74ls47

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watzmann

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Hi All ,

i have built a circuit that connect pic16f84a 74ls47 and a coomn anode seven segmant.

i have a aproblem now that all the inputs of the 74ls47 gives 1.3 volts , i don't why.

for that reason my pic ports that connected to the 74ls47 is also 1.3 volts , even if i removed the pic IC .

i'll load the photo of that schematic and please tell me what's wrong.

thank you
 

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watzmann said:
Hi All ,

i have built a circuit that connect pic16f84a 74ls47 and a coomn anode seven segmant.

i have a aproblem now that all the inputs of the 74ls47 gives 1.3 volts , i don't why.

for that reason my pic ports that connected to the 74ls47 is also 1.3 volts , even if i removed the pic IC .

i'll load the photo of that schematic and please tell me what's wrong.

thank you
hi watzmann,
Without the PIC connected, the inputs of the 74LS47 will assume/pullup to a high input, about 1.5+V.
It sounds as though when you have the PIC connected, you have not set PORTB as an output???:)
 
so you mean that that is normal , and i have to set up my portb to be as output ?

i did soemthing else i made all the portb to be low but nothing happen , anyway i'll try now to set my port b to be output and tell you
 
watzmann said:
so you mean that that is normal , and i have to set up my portb to be as output ?

i did soemthing else i made all the portb to be low but nothing happen , anyway i'll try now to set my port b to be output and tell you

hi,
The about, 1.5V is normal for a open input pin on a 74LS series ic.

In the PIC you must set the pins connected to the 74LS as outputs.

Can you post your program?.
 
hi,
Looking at the bit of drawing you have posted, I dont see any connection to the 74LS47, 4 [rbo] and 6 [rbi]
I connect pin 4 to +V and pin 5 to 0V, leave pin 3 floating.
 
so you mean that that is normal , and i have to set up my portb to be as output ?

i did soemthing else i made all the portb to be low but nothing happen , anyway i'll try now to set my port b to be output and tell you
 
watzmann said:
now i said in my program to let all portb as outputs ,

but it still indicate 1.3 volts ,

!!!!!
hi,
Please post your program.:)
 
i'm using picbasic
---------------
DEVICE=16F84A
XTAL=4
TRISB=%0000000
TRISA=%0000000
HIGH PORTB.0
HIGH PORTA.4
-------------
 
watzmann said:
i'm using picbasic
---------------
DEVICE=16F84A
XTAL=4
TRISB=%0000000
TRISA=%0000000
HIGH PORTB.0
HIGH PORTA.4
-------------
hi,
The 7447 is wired to pins 7,6,5,4 according to the circuit.

Why do you think setting PORTB.0 HIGH make a change on the 7447 input?:)
 
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