I recently debugged the WIFI module and found that the same signal line has two options: pull-up and pull-down. Of course, it is determined by the different chips connected, but which parameter depends on the pull-up and pull-down?
One, the WIFI chip is different, one is pulled up and the other is pulled down, that is, the output stage has different current requirements? How do friends understand the pull-up and pull-down? Can you help me summarize? I have been looking for information, but I still don't understand it very well.
Hatcher Posted on January 11, 2021
From the figure, you can see that both of these are weak pull-ups. It may be to prevent the input signal from needing a specific high and low level when the system is Idle to prevent internal oscillation. The other (not your case) is due to open drain , It needs to be pulled up, and the value of the pull-up resistor needs to be calculated. Generally if point-to-point does not need to be calculated, 4.7K or 10K can be used, but if it is point-to-multipoint, you need to consider the output terminals Vol, Iol, and input terminals IIH , IIL, Vih, Vil, etc.
Please go to TI website, or google, pull high resistor calculation, there are calculation formulas in such articles, but you need to understand the content of the formula carefully when you have the formula.
Aina Posted on January 11, 2021
In the figure, the pull-up and the bottom-connection do not have the same signal line. AP6210
Corbett Posted on January 11, 2021
My understanding is that some of the control pins of the digital chip cannot be left floating, which is an indeterminate state, so the initial state must be given a state. This state is high and low. The pull-up means the initial state is high, and the pull-down is the initial state. Low, the resistance value is calculated by his current.
