Pull-up resistor question / data lines

[caphair]

Re: Pull-up resistor question / data lines

01005 resistors are smaller than a pepper spec. You got guts measuring this!

Notice your schematic net labels tell if a signal is an input or output or bi-directional.
The body outline has an arrow: <- OUT, -> IN, <> BI for bidirectional lines. Bubble symbol means, example on RESET and IRQ, pulled low to assert.

A MCU input can have a pullup or pulldown resistor or nothing- this is assigned in firmware.
Pullup resistors are used on open-drain (driven) signals like RESET or IRQ because several IC's can activate (pull low) the line. It is a "wired-OR" setup. This IC or that IC can pull RESET low, for example.

A MCU output can be push-pull or open-drain.

For that iPhone, I think those are open-drain MCU signals (RESET and IRQ), so they need pullup resistors to +1V8.
They should stay high unless pulled low by anybody connected to cause RESET. BUT during off/sleep I think the +1V8 is switched off so it is confusing.

Lol yeah it's very tiny I have microscope I use for this. Helps tons.

Thanks for the tidbit about the bubble symbol, never noticed it before.

iPhone schematics are confusing, they seem vague compared to most other schematics im used to.

The previous model used reset in similar function for multiple perifperals, low to reset, high active. This model has a reset and active/ready lines so makes things more complicated to understand.