Retro-engineering the FXL8 switcher : footswitch board

Okay, I had some time ahead so I looked into the FXL8 switcher to try to guess how it works.

It is driven by a STC 89C52RC micro controller (8051 core) in a PQFP-44 package.
Its datasheet (in Chinese) is here : http://pdf1.alldatasheet.com/datasheet-pdf/view/139744/ETC1/STC89C52RC.html

The main footswitches are linked to the main board by a 6 cable connector. Pins are :

From top to bottom : pin 0...5

- Pin 0 : ground (it's bit odd since the ground is not used anywhere on the footswitch board)
- Pin 1 : connected to SW_B, SW_C, SW_D
- Pin 2 : connected to SW_MINUS, SW_PLUS, SW_A
- Pin 3 : connected to the other end of SW_A, SW_D
- Pin 4 : connected to the other end of SW_PLUS, SW_C
- Pin 5 : connected to the other end of SW_MINUS, SW_B

Footswitch board schematic

Two strange this (IMHO) :
- The switches look like Alpha DPDT momentary switches. a simple SPST momentary switch would have been enough (reminds me of 3PDT footswiches in some of non-true bypass EHX pedals :-)
- Why use a ground pin (pin 0) ? It isn't connected to anything on the board.
- As a beginner, I would have use one pin per switch instead of making a complex multiplexed system...

Quality footswitch :)