You will also hear of "Weak" and "Strong" pullups: this reflects how "hard" the pullup can "pull" - ie, how much current it can deliver.
A low-value resistor provides a "Strong" pullup.



is there any thumb rule that you use strong or weak pull up .. how do we decide when to use what .. please be kind enough and explain us with an example ...
usually i have used 1K , 2.2K and 4.7K as standard pull up values without much botheration ...
usually i use 1K in keypad pull ups ... 2.2K with open collector IC's other than controllers and i use 4.7K with 89C51 family controllers on P0.... am i right?
please through some more light on it ...
also when do we have to be very careful while deciding on these values and how do we decide on the current flow ... ( looking for a valid answer and not like please refer to the fan in of the respective IC)... if you can refer and guide me to a good site which explains this clearly .... and i have gone through the forum discussion before posting this query ...
also do we have to really worry about the pull up value ?? is there any safe value ???
thanks and regards
nitin