add basic wiring information
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# keyplus mini beta
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## Errata rev2
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The SS and MO pins are mislabeled. The SS pin should be MO, and the MO pin
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should be SS.
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## Wiring
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### Wiring key matrix
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The key matrix should be wired to the ROW and COL pins on the PCB. Wiring of the
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ROW and COL and column pins should start from the lowest number pin (i.e. `ROW0`
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and `COL0`) and work up in consecutive order. The diodes in the key matrix should
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point from the COL to ROW pins (other scan modes not implemented yet).
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The `COL15, COL14, COL13, COL12` pins (underlined on the PCB) may also be used
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as `ROW` pins. They map to the following row pins:
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* ROW6: COL15
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* ROW7: COL14
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* ROW8: COL13
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* ROW9: COL12
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Thus it is possible to have up to 120 keys connected using a 10x12 matrix.
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### Wired split with I2C
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To connect to boards with I2C for wired split, connect the 5V, SDA, SCL, and
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GND pins between devices. You can connect several devices in this manner, they
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just need to share 5V, SDA, SCL and GND pins.
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I would recommend **NOT** using TRRS connectors for wired split. While connecting and
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disconnecting the device the contacts inside the TRRS cable can short to one
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another. Instead I would recommend using micro USB ports, or another
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connector that doesn't short it's contacts when it is plugged/unplugged. Then
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you will be able to take advantage of the wireless/wired hot plugging
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functionality without worrying about damaging the hardware. You can find
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male-to-male micro USB cables online with a bit of searching.
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### Wireless with nRF24L01+
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To use wireless mode, you will need a battery and a nRF24L01+ module. The
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battery should be 3V. Some options for the battery are 1xCR2032, 2xAA/AAA, or
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1xAA/AAA with a boost converter. Note the keyplus mini controller does not
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support any sort of charging of the batteries. When there is no USB connecting
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the device will run off battery power. When the USB is plugged in, it will
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automatically switch to run off USB power. To connect the battery connect:
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* BAT -> positive battery terminal
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* GND -> negative battery terminal
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To connect an nRF24L01+ module you will need to connect these pins:
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* xmega -> nRF24L01+
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* R0 -> CE
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* R1 -> IRQ
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* MO -> MO / MOSI (Note: rev2 PCB use SS instead)
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* MI -> MI / MISO
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* SS -> SS / CSN (Note: rev2 PCB use MO instead)
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* SCK -> SCK
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Note: currently the IRQ pin is not used in the code, but I'll add code to take advantage of it soon.
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### PCB schematic for rev 2
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[Schematic for keyplus mini](https://rawgit.com/ahtn/keyboard_pcb/bb20b354216aa1858254db9946aa67aa8df67bfd/keyplus_mini/rev2/keyplus_mini.pdf)
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### Mechanical information for rev 2
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## Layout file format and programming
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TODO
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For the mean time, refer to the [example layouts](https://github.com/ahtn/keyplus/tree/master/layouts), and the [list of available keycodes](https://github.com/ahtn/keyplus/blob/master/host-software/layout/mapped_keycodes.py#L8).
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## Current firmware limitations
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Firmware is still in beta and several features are not completely
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finished yet. Some prominent ones:
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* Macro and hold keycodes can't be used in the layout config file yet.
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* No LED support yet (including indicators)
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* Pairing unifying mouse is not exposed to devices yet
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## Testing key matrix
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The firmware supports a mode where it will pass the raw keyboard matrix data to
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the PC. This can be used to check the row and column pairs in your key matrix.
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Currently, this can only be used on the command line using a python script
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[`keyplus/host-software/keyplus_cli.py`](https://github.com/ahtn/keyplus/blob/master/host-software/keyplus_cli.py).
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To use the keyboard matrix passthrough mode, run `./keyplus_cli.py passthrough`
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and you should see output like this:
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```
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$$ ./keyplus_cli.py passthrough
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r3c5
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r3c0
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r1c0
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r0c1
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r0c1 r1c1
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r1c1
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r1c1 r3c3
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r3c3
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```
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Where each line shows which keys in the matrix are currently being pressed.
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Note only devices directly connected by USB will report key presses using
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passthrough mode.
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## xusb bootloader
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The bootloader installed on the ATxmega is the [xusb bootloader](https://github.com/ahtn/xusb-boot).
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To enter bootloader mode press the reset button (or short the RST and GND
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contacts) once when the USB cable is plugged in. The device will remain in
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bootloader mode until it is programmed, or until the reset button is pressed a
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second time. For a more detailed explanation of the bootloader, [see
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here](https://github.com/ahtn/xusb-boot#ways-to-enter-the-bootloader).
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The lock bits on the ATxmega have been set to disable reading from flash by an
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external programmer. This is done to protect the encryption keys that are
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stored in flash. Also, for security reasons the bootloader will wipe SRAM on
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power up.
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## Trouble shooting
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* Make sure that the battery contacts have a firm connection. I've had issues
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sometimes with my homemade CR2032 holders where vibrations from typing would
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cause the contacts to be unreliable.
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