PICOBOOT IPL SO signal

[rowenback]

Hi,

I try to understand how the picoboot can work regarding SO pin of GC IPL chip.
Il seems that at boot time, the RPI Pico and the GC IPL chip get the CS, CLK signal, so both of them should drive the SO pin.
But that is not possible, 2 chips cannot drive the same pin without a nice smoke.

Moreover, when installing the picoboot, the EXTIN pin of the BBA connector shall be connecte to the ground ? What for ?

Can anyone bring me some light ?

Regard.

Christophe.

[Papy.G]

On SPI bus, every peripheral device is connected in parallel to the SO line, each one talking when its turn arrives.

Don't you pull the IPL's CS pin up to solder it to a wire in the install process?

ExtIn may stand for External interruption, so it may be just to halt the IPL and allow the Picoboot to hook into the boot process.

Wild guess…


High speed SD adapters seem to have something to do with permanently hooking down an interrupt pin too, wonder if it is related…

[rowenback]

I agree with you about: On SPI bus, every peripheral device shall be connected in parallel to the SO line
But when mounting the picoboot chip you shall also connect in parallel the CS signal. This is the reason i do not understand how it can work.

Regarding EXTIN of BBA , for me it is not really for interrupt, it is a pin which indicates if the device is plugged.
Moreover the BBA has also a INT pin dedicated to interrupt different from EXTIN.
On BBA device the EXTIN pin is internally connected to GND, so when you plug the device, the EXTIN pin go to the ground GND and the GC know that a device was plugged and he can also know when you unplug it.

So i still do not know how this can work.