Simulator Reference: State Machine

Netlist entry

Axxxx [ in_0 in_1 .. in_n ] clk reset [ out_0 out_1 .. out_n ] model_name

Connection details

Name	Description	Flow	Type	Vector bounds
in	Input	in	d, vector	none
clk	Clock	in	d	n/a
reset	Reset	in	d	n/a
out	Output	out	d, vector	1 - no upper bound

Model format

.MODEL model_name d_state parameters

Model parameters

Name	Description	Type	Default	Limits
clk_delay	Delay from CLK	real	1nS	none
reset_delay	Delay from reset	real	1nS	none
state_file	State transition specification file name	string	none	none
reset_state	Default state on RESET & at DC	integer	0	none
input_load	Input loading capacitance (F)	real	1pF	none
clk_load	Clock loading capacitance (F)	real	1pF	none
reset_load	Reset loading capacitance (F)	real	1pF	none
family	Logic family	string	UNIV	none
in_family	Input logic family	string	UNIV	none
out_family	Output logic family	string	UNIV	none

File Syntax

The following is a formal description of the state machine file syntax using Backus-Naur form (BNF). '{' and '}' mean "zero or more" of the enclosed items.

state_machine_def :: state_def { state_def }

state_def :: header_line { continuation_line }

header_line :: STATENUM outputs inputs SEPARATOR STATE_DEST

continuation_line :: inputs SEPARATOR STATE_DEST

outputs :: OUTPUT_VALUE { OUTPUT_VALUE }

inputs :: INPUT_VALUE { INPUT_VALUE }

STATENUM :: 0 based integer indicating state number.

SEPARATOR :: Any sequence of characters but not whitespace. '->' is conventional

STATE_DESTINATION :: integer indicating state number.

OUTPUT_VALUE :: two digit sequence to define one of the 12 output states. First character can be 0, 1 or U. Second character can be s, r, z or u for 'strong', 'resistive', 'high-z', and 'undefined' respectively.

INPUT_VALUE :: 0, 1, x, or X

The idea is to have N state_def's where N is the number of states. Each state_def has one header_line and a number of following continuation_lines. Both define the destination state for a given combination of inputs. The header_line additionally defines the state being defined and the output value for that state. Header lines and continuation lines are distinguished by counting the tokens. The system does currently not appear to fail gracefully if this is wrong. A header_line should have (num_inputs+num_outputs+3) tokens and a continuation_line should have (num_inputs+2).

The number of inputs and outputs is defined in the netlist line which is in the form:

Axxx [ inputs ] clk reset [ outputs ] modelname

Notes

Currently this model is unsupported as it has not undergone testing or analysis. It is part of the original XSPICE system and should be compatible with other implementations but this cannot be guaranteed.

The following is an example of a state transition specification file

* This is a simple example of a state machine state file
* It is a 2 bit up down counter with synchronous reset

*Present    Outputs     Inputs                State destination
*State      for state   (reset, up/down)
0         0S   0S       0       0                -> 3
0       1                -> 1
1       0                -> 0
1       1                -> 0
1         0S   1S       0       0                -> 0
0       1                -> 2
1       0                -> 0
1       1                -> 0
2         1S   0S       0       0                -> 1
0       1                -> 3
1       0                -> 0
1       1                -> 0
3         1S   1S       0       0                -> 2
0       1                -> 0
1       0                -> 0
1       1                -> 0

See Examples/Digital_Devices/state_updown.sxsch