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pull-up resistors for PIC18F

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free_f0x

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well , i read the threads related with my questions i think i need to ask two more questions

1) im using the circuit below and when im connecting pull-up or pull down resistor the system not working ! , i know that PORTB in PIC18F4550 has internal resistors but even when i connect resistors to PORTD system in not working as it should be.

2) why do people prefer to use 0 as input to activate their pin ( i mean sinking mode)

Thank you

check the circuit there
http://media.tripod.lycos.com/preview/3250826/1024x1024-1745623.png
 

FvM

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1) im using the circuit below and when im connecting pull-up or pull down resistor the system not working ! , i know that PORTB in PIC18F4550 has internal resistors but even when i connect resistors to PORTD system in not working as it should be.
"Not working" is in fact a vague information. I understand, that the circuit is intended to use internal pull-up resistors (also Port D has it). If programmed correctly, which is the critical point, I guess, it will work.

The fact, that PIC18 only has weak pull-up but no pull-down resistors suggests to use them with active low switches, as the present circuit does. Isn't it?
 

qwertyuiop415263

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you should use pul lup resistors (10k)with portD when you want to interface mechanical switches.
when you want to use a certain pin as an input you have to load Tris Register with 1
 

free_f0x

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"Not working" is in fact a vague information. I understand, that the circuit is intended to use internal pull-up resistors (also Port D has it). If programmed correctly, which is the critical point, I guess, it will work.

The fact, that PIC18 only has weak pull-up but no pull-down resistors suggests to use them with active low switches, as the present circuit does. Isn't it?
ok , in short speech , when i power the system without any pull-up resistors for PORTD it will work, but when i use pull-ups it will not.
no working :im not able to receive logic 1 when i press any switch connected to PORTD.

PS: system is working nicely, i want to understand the behavior of the chip.

---------- Post added at 19:15 ---------- Previous post was at 19:13 ----------

you should use pul lup resistors (10k)with portD when you want to interface mechanical switches.
when you want to use a certain pin as an input you have to load Tris Register with 1
when i load 10k im not able to receive logic 1, when i remove it system will be happy! im trying to understand why!
 

FvM

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Apparently, something is wrong in your real circuit, but it can't be seen from the schematic.
 

free_f0x

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Apparently, something is wrong in your real circuit, but it can't be seen from the schematic.
Thank you for reply FvM

the circuit is working with no one problem i post this just to make more understanding of chip behavior, i re-check the circuit seems ok
 

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