cablescomputersusbusb-cusb-host
I have wired some custom USB-C cables from scratch in the past, where the USB-A connector is plugging in to a host PC. If I wired a USB cable where the USB-C connector was plugging into a host receptacle (a USB-C to Mini-USB cable for example), would there be any additional wires/pins that need to be connected in order for the cable to function properly? Typically, I am using a 4-wire cable, connecting VBUS, Ground, D+ and D- pins.
Thanks in advance!
The USB 3.1 specification spells out exactly how to make this, and any other USB C -to- USB legacy cable. For a USB-A (2.0), the connection looks like:
To solve your problem of interconnect, you need to define the function of your cable. The distinction between "A" and "B" variants (be it classic Type-A or B, or their mini/micro variants) is specifically to determine which one goes to host, and which goes to a device. The cables of this sort must be always of A-B type, not B-B.
The tablet device, if it is a strictly host, must have Type-A receptacle, micro or normal. To fit in, the cable end must be of squarish Type-uA, with ID pin grounded.
If the tablet has OTG functionality (which is likely), the ID pin ground makes the tablet to turn into HOST mode. If ID is floating, it will/should act as DEVICE.
Now, it become a common practice in tablets to use micro-B receptacles, and not micro A/B, even if the tablet's port has dual-role functionality. To make such tablet to be a host, people have invented "OTG adapters", which have u-B shape on one end, but has the ID pin grounded , and Type-A receptacle on the other end. Then you can use a standard Type-A to mini-B cable to connect to the old keyboard. Or you can try to solder a u-B connector and ground its ID pin, but it would require the overmold disassembly, and might be difficult. Alternatively you can get a cable with u-A end (square shape), and file off proper corners of its shroud, to make it fit into angled u-B receptacle. Then connect VBUS, GND, D+ and D- to your mini-B keyboard cable.
Since the keyboard is likely a Low-Speed device, no special care or workmanship is required to make this cable connection.
Best Answer
If you want the cable to act as Type-C host to mini-B plug (to plug into a device with mini-B receptacle), you should connect A5 pin to ground via 5.1k 5% resistor inside the Type-C overmold. This will inform the Type-C host that the cable is "a device". Although the mini-B is not in the official list of allowable cables in Type-C specifications, you can use the wiring schema for Typ-C to micro-B plug, it is there, and mini-B is one-to-one wired to micro-B.