Connecting extra pins for Raspberry Pi Zero W ICSP control
I've been looking at the instructions in https://manual.prusa3d.com/Guide/0.+Preparing+necessary+components/585?lang=en#s9664 , which seems to recommend connecting only some of the pins, nRESET, VCC, GND, TxD, RxD.
I would like to experiment with a full ICSP connection, and run avrdude on the Raspberry Pi to be able to reprogram the bootloader.
How safe would this be in terms of 5v / 3.3v compatibility between the Einsy RAMBO and the Raspberry Pi?
The Einsy schematics at https://github.com/ultimachine/Einsy-Rambo/blob/1.1a/board/Project%20Outputs/Schematic%20Prints_Einsy%20Rambo_1.1a.PDF shows the Raspberry Pi connector at sheet 5, clearly indicating the ICSP pins, but it is not clear whether the ICSP pins are meant to be driven by the Raspberry Pi, or is this a dual-use connector.
On Sheet 3, I can see that the MOSI and SCK pins are connected via 22 ohm series resistors and 120ohm ferrites, while MISO is connected as-is.
Are these resistors there in order to protect 3.3v devices on ICSP?
Re: Connecting extra pins for Raspberry Pi Zero W ICSP control
Does this help:
https://www.raspberrypi.org/documentation/usage/gpio/
https://www.raspberrypi.org/magpi/pi-zero-gpio-expander/
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Chuck H
3D Printer Review Blog
Re: Connecting extra pins for Raspberry Pi Zero W ICSP control
Upon closer reasing, it seems that this is clearly a dual/triple-use connector, and it is definitely NOT safe to connect all the pins to the Raspberry Pi.
Just looking at J19 pin 1 with its 12V supply clearly shows this is not intended to be connected directy to the Raspberry Pi.
More to the point, J19 pin 12, (MOSI) is mapped to GND on the Raspberry.
So, it seems I cannot hook this up directly as-is, perhaps hacking the connection to some other Raspberry Pi pins via a diode.