Ladder Diagram Design : Huffman Method

Huffman method is classical method for planning a sequential system. This method is more complicated but the result will have a minimal relay. 

There are two kinds of state, Stable and Unstable. Stable state is where the output state is equal to input state. While unstable state is transition where the output is not same as input.

Procedures

Example

1. Build primitive flow table
   First, create a table with number of columns is 2^n, where n is number of input. Also add other column at the left for all state and at right for the output.
   
   
   Then fill each stable and unstable state also the don't care state.
   
   
2. Merged flow table row
   Need to merge because it will decrease the number of components.
   
   
3. Create state
   To avoid race, there is an important rule to ensure only one state is changed each moving state.
   
   The state flow are,
   
4. Decrease excitation
   Y1
   
   Y2
   
   And the Set Reset function are,
   
   And the output function for A+ is
   
   
5. with that output function, it will looping forever, so add a "START" to S1 and modify the output function to,
   
   so the final output function is, 
   
6. Draw the Ladder Diagram
   

   

Reference:

[1] PPT System Automation (M. Rameli & Eka Iskandar)