Hello i have designed a small device that plugs into my phone's (type C) usb and reads/writes text data to an android app i created.
Each device must be programmed after assembly. The PCB has a header connector that traces to the uC's SPI port, through which i do the initial programming with avrdude from my computer.
Now i wanna ditch the SPI header connector (6 lines) and use the superfluous lines of the type C connector to reach the uC's SPI interface.
My device uses VBUS, GND, D+, D-, and CC1 to communicate with my phone. I wanna use the "extra" type C lines for programming (VCC, G, MOSI, MISO, CLK, RESET) and wire up a female type C connector that has MOSI<->SBU, MISO<->SBU, CLK<->TX1+, RESET<->TX1-.
Anybody see any problems with this plan? i don't know the impedance of the TX1 lines.

 

Officially you're not allowed to use those pairs for something else until after you've negotiated an alternate mode. You can probably get away with it if you don't mind not being standard compliant.

The other possibility is to use debug mode. You either pull both CC lines high, or both low. That can never happen with a normal USB-C cable because such cables only have one CC line wired. In debug mode, you can basically do anything you want. In principle your special debug mode signals shouldn't be drive when not in debug mode, but again, you can probably get away with it if you don't mind not being standard compliant.

 

Officially you're not allowed to use those pairs for something else until after you've negotiated an alternate mode. You can probably get away with it if you don't mind not being standard compliant.

well it is a commercial product, but it doesn't come with any claim of being standard compliant. However, if i plug it in and the USB port or the android OS gets an attitude, could that interfere with the communication between the device and my app?
when i plug it into the phone, the connections will be:

phone device
------- -------
TX1+ -- HiZ
TX1- --- HiZ
SBU --- HiZ
SBU --- HiZ tied high by 10k

thanx, mike

 

Nevermind.... I was wrong and deleted it