The right and left hand sides are connected using
 a standard ethernet patch cable. The cable cannot
 be crossed!!! If you cannot make one yourself then
 buy a shortest patch cable you can get. The longest
 cable I tried had 110 cm.


Connection of right/left hand side pin headers to
 the RJ45 ethernet jacks:
RJ45 | Ethernet | Cable      | K80CS         | PinHeader
pin# | meaning  | color      | meaning       | pin#
-----+----------+------------+---------------+------
1      tx+d1     whiteGreen   iData            (1)
2      tx-d1       Green      CLK1 (often L)   (2)
3      rx+d2     whiteOrange  iAnalogY         (-)
4      bi+d3       Blue       CLK0 (mostly L)  (3)
5      bi-d3     whiteBlue    iAnalogX         (-)
6      rx-d2       Orange     GND              (4)
7      bi+d4     whiteBrown   oLoad (often H)  (5)
8      bi-d4       Brown      Vcc              (6)
http://en.wikipedia.org/wiki/Ethernet_over_twisted_pair#Cabling
The RJ45 socket type is: TE CONNECTIVITY / AMP  5556416-1  JACK


The physical keyboard matrix:
* we drive rows and scan one column at a time

Right hand side ColRow Numbering:
   14 24 34 44 54 64 74
   13 23 33 43 53 63 73
   12 22 32 42 52 62 72
04 11 21 31 41 51 61 71
03 10 20 30 40 50 60 70
02 01 00

The left hand side is a mirror image.

Proposed cable length
 * 8 wire ethernet cable: 25 cm
 * 16 wire ribbon cable: 12 cm
 * 6 wire ribbon cable: 14 cm