3 How to Configure a State Machine

InterConnect Studio (ICS) is the software used to configure a TPLD. Once ICS is launched and a device is selected adding a state machine to the design enables configuration of the dedicated state machine block. Figure 3-1 shows the default configuration when the state machine is added. To add additional states click the plus icon highlighted in Figure 3-1. The only input to the state machine by default is the NRST input. This input is active low and causes the state machine to revert back to the initial state. By default this is st0 and this input is asynchronous even when the synchronous mode of the state machine is selected.

The state options in this state machine are name, output value, and transitions from shown in Figure 3-2. The Name configurable simply adjusts the reference of the state in the SM view and the configuration space, but has no affect on the actual design. Output value is a hex representation of the binary values present at OUT7 - OUT0 while the state machine is in that state. Each output can be connected to an internal port, or routed to output pins for external use. The Transitions From drop-down menu enables the transitions from one state to another. In this drop-down menu selecting any option adds a transition from the option into the current selected state For example, if the current state selected is st0, selecting st1 in that drop-down menu creates a transition event from st1 to st0 as shown in Figure 3-3.

Creating the transition events is not enough to cause the state machine to transition the state also needs a trigger to spark that transition. Figure 3-4 shows a very basic implementation of the SM at work. NRST is tied to POR so the state machine never resets. Once pin0 goes high this state machine transitions out of it's default state st1 into st0.