All the outputs are inverted,
   clock and strobe are rising edge triggered

  The wiring is as follows:

  Data Line 0  -> Shift register data
  Data Line 1  -> Shift register clock
  Data Line 2  -> Output Latches (strobe)


  To send a 0

   data  X_____X
   clock ___-___
   strobe_______

  To send a 1

   data  X_---_X
   clock ___-___
   strobe_______

  To move the shift register data to the outputs

   data  XXXXXXX
   clock _______
   strobe___-___


  The shift regiter works like a bucket brigade.
  bits are always passed to the first register.
  on each clockpulse, the bit in all
  the shift registers gets passed down 1.


  data ->  reg1 -> reg2 -> reg3 -> reg4 ...


  so in this example to get a result of:
    reg1 1
    reg2 0
    reg3 0
    reg4 0

  the following would be done:
    - shift in a 0 (this ends up in register 4)
    - shift in a 0
    - shift in a 0
    - shift in a 1

Chaining:
  Here is how the port numbers go when devices are chained:

[master] 
  |
  V
[slave1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16] 
  |     1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 
  V
[slave2 1  2  3  4  5  6  7  8  9  10 11 12 13 14 15 16] 
        17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 



To send a 0:
  - set the  data low
  - set the clock high
  - set the clock low

To send a 1:
  - set the data high
  - set the clock high
  - set the clock low

To strobe the outputs:
  - set the strobe high
  - set the strobe low

There are a few ways to do this, if you have programming access to the io
port, then you can output these number to the port, keep in mind that all 
the bits are inverted, so high is 0 and low is 1

 Here are all the combinations you need:
 data low, clock low, strobe low   = 7 
 data low, clock high, strobe low  = 5
 data high, clock low, strobe low  = 6
 data high, clock high, strobe low = 4
 data low, clock low, strobe high  = 3

If you dont have binary access to the printer port, you can also
operate the controller by "printing a text file"
Because the other bits are ignored, we can use ascii characters,
which have the same binary patterns.

this is done in a similar manner to the binary control.

for example to shift in a 1 and 0 and then strobe you would 
print the following text to the controller:

64675737

the 646 sends a 1
the 757 sends a 0
the 37  strobes the shift registers into the outputs.

make sure there isn't a carrige return or line feed at the end 
of the file or you will get extra signals that will probably 
mess things up on ya.