Serial Mouse Converter
======================
This makes old serial mouse into modern USB one.

https://github.com/tmk/tmk_keyboard/wiki/Serial-Mouse



Pinout
------

    DE-9   DB-25    Mouse     DCE     DTE     MAX232    MCU
    ---------------------------------------------------------
    1                         CD      CD
    2      3        Data      TXD     RXD     ->        PD2
    3      2        V-        RXD     TXD     <-
    4      20       V+        DTR     DTR     V+
    5               GND       GND     GND     GND       GND
    6                         DSR     DSR
    7      4        V+        CTS     RTS     V+
    8                         RTS     CTS
    9                         RI      RI
    -      --                 ---     ---     VCC       VCC



Wiring
------
Mouse TXD, RXD, DTR and CTS should be wired to RS-232 driver.
Wire up RS-232 driver charge pump output V+ to DTR and CTS for power source purpose.
Connect Mouse TXD to AVR PD2(RXD) *through* RS-232 driver for mouse data.



RS-232 Driver
-------------
Some mouses can require higher voltage for power source.
SP3233E outputs only +-6V at charge pump output and didn't work with Microsoft green-eyed mouse.
ADM232A works for both Microsoft green-eyed mouse and DELL serial mouse.



Build Setting
-------------
defined in config.h and Makefile.

### Microsoft protocol
1200 baud, 7-bit data, no parity, 1-bit stop, lsb-first

### MouseSystems protocol
1200 baud, 8-bit data, no parity, 1-bit stop, lsb-first(Not tested)
