State Machine

The digital state machine provides for straightforward descriptions of clocked combinational logic blocks with a variable number of inputs and outputs and with an unlimited number of possible states. The model can be configured to behave as virtually any type of counter or clocked combinational logic block and can be used to replace very large digital circuit schematics with an identically functional but faster representation.

The DSTATE model is configured through the use of a state definition source text. The file defines all states to be understood by the model, plus input bit combinations which trigger changes in state. An example source text is shown below:

* This file defines a simple 2-bit counter with one input. 
* The value of this input determines whether the counter 
* counts up (in = 1) or down (in = 0).
*STATE D0 D1 I0 -> NEXT

 0     0  0  0  -> 3
             1  -> 1

 1     0  1  0  -> 0
             1  -> 2

 2     1  0  0  -> 1
             1  -> 3

 3     1  1  0  -> 2
 3     1  1  1  -> 0

Several attributes of the above source text structure should be noted. First, ALL LINES IN THE FILE MUST BE ONE OF FOUR TYPES. These are:

1. A comment, beginning with a "*" in the first column.
2. A header line, which is a complete description of the current state, the outputs corresponding to that state, an input value, and the state that the model will assume should that input be encountered. The first line of a state definition must ALWAYS be a header line.
3. A continuation line, which is a partial description of a state, consisting of an input value and the state that the model will assume should that input be encountered. Note that continuation lines may only be used after the initial header line definition for a state.
4. A line containing nothing but whitespace (space, newline).

A line which is not one of the above will cause a file-loading error.

Note that in the example shown, whitespace (any combination of blanks, tabs, commas) is used to separate values, and that the character "->" is used to underline the state transition implied by the input preceding it. This particular character is not critical in of itself, and can be replaced with any other character or non-broken combination of characters that you prefer (e.g. "==>", ">>, ":", "resolves _to", etc.)

The order of the output and input bits in the file is important; the first column is always interpreted to refer to the "zeroth" bit of input and output. Thus, in the file above, the output from state 1 sets out[0] to "0", and out[1] to "1".

The state numbers need not be in any particular order, but a state definition (which consists of the sum total of all lines which define the state, its outputs, and all methods by which a state can be exited) must be made on contiguous line numbers; a state definition cannot be broken into sub-blocks and distributed randomly throughout the file. On the other hand, the state definition can be broken up by as many comment lines as you desire.

Input Values

Output Values

Parameters

Error Messages