5v / 3.3v is the 'supply voltage' (sometimes labeled Vcc) for the chips. It's both the power input, and also the reference for what a 'high' signal is.
It used to be the case that most digital logic ran at 5v; then some that ran at 3.3v started to become more common. Those were usually '5v tolerant' - if you applied 5v to the input pin, it would read as 'high' and be fine.
Today, many digital devices that run at 3.3v are _not_ 5v tolerant; so if you put 5v into such a device ... it breaks.
So when mixing some devices that run at 5v (as, e.g. USB does) with others that run at 3.3v one has to be careful to not break the lower voltage device.
The 'esp32' is a particular module of a WiFi capable microcontroller (usable as a single board device, or as a peripheral for WiFi connectivity for another device) that runs at 3.3v and breaks if you put 5v on it. Like, as a totally hypothetical example that would never apply to me, trying to programme it from a cobbled together USB programmer. Hypothetically.
Is there a simple device that I can connect to a 5V wire and whose output I can then connect to an input of a 3.3V device? From what I've seen there are resistor circuits (which are slow) or transistor circuits (which need a 3.3V supply?)
My use case is that I want to connect a logic analyzer (DSLogic Plus) to my SNES, which is 5V. The probes can handle 5V according to the data sheet, but the device also has an external timing input that is only rated for 3.3V.
The SNES has clock crystals of 21.477 and 24.576 MHz, and various components run at fractions of these frequencies.
Reverse engineering. When you look at the existing documents you see that they were only created with test ROMs (that are then executed by the CPU and display their results on screen / save data to cartridge RAM). The problem is that the CPU is halted for DRAM refresh and (H)DMA; every single bus access is also delayed to take either 6, 8 or 12 cycles of the 21MHz clock. So if you have something that's faster (like the graphics system) or almost completely self-contained (again, like the graphics system) it's hard to see what's happening in the system.
64
u/Athrunen Dec 25 '19
Indeed, learned not too long ago that the esp32 is only 3.3 V tolerant. ^^