The XViCO board is based around an STM32F103RCT6, a 64-pin part.
10 - Extruder (hotend) Temp
11 - Bed Temp
34 - "Level"
38 - X Home
41 - Y Home
42 - "TX" on header. Function: USART1TX
43 - "RX" on header. Function: USART1RX
44 - Z Home switch (also USBDM, but not brought to header)
45 - E Home (filament runout?) (also USBDP, but not brought to header)
46 - "DO" on header. Function: JTMS-SWDIO
49 - "CK" on header. Function: JTCK-SWCLK
L5970D - 12V to 5V Buck regulator
LD1117 - 3.3V Linear regulator
Winbond 25Q64JVS10 - 64Mbit SPI Flash
BUP_5V header - connected to 5V rail and GND
FirmwareI desoldered the Winbond flash device and dumped the firmware here. The STM32F103RCT6 firmware is here (many thanks to advice from Samuel Pinches!)
I looked for images in the firmware using Irfanview (thanks to this very handy blog entry!) and eventually, this image jumped out:
Well, that's something to go on! After some googling, I landed at another blog, which seemed to explain the situation well.
The logeek.cn site has schematics for an STM32F103-based 3D printer board, it's for a much more sophisticated unit. I suspect the XViCO board is cut down significantly from the original design.