3.4.1 Hardware State Machine Example - Candy Dispenser

For example, consider a simple Moore State Machine, as shown in Figure 3-3 operating a coin-based candy machine. Figure 3-4 shows a pictorial representation of the state machine and the circuit-level implementation using the Signal Routing Port and CLC peripheral. Hardware State Machines with Signal Routing Ports shows the Signal Routing Port setup.

Figure 3-3. State Diagram of a Candy Dispenser

Figure 3-4. State Machine Representation of a Candy Dispenser

Tip: In devices where the signal routing port pin output is available as a PPS output option, the RW0 output can be routed directly to the physical I/O pin, eliminating the need for the CLC2 peripheral in this example.

Hardware State Machines with Signal Routing Ports

// Input to SRPORT: CLC1 Output (next state)
// Output from SRPORT: PPS input to CLC2 (current state)
// Note: Initialization routines are not shown

void HardwareStateMachine_SRPORT()
{
    // Set RW0 input as CLC1
    PORTWIN0 = 0x08;        // 0x08 = CLC1 on PIC18F46Q71

    // Set RW0 as feedback input CLCIN0 for CLC1
    CLCIN0PPS = 0x38;       // 0x38 = RW0 on PIC18F46Q71

    // Optional: Set RW0 as current state input CLCIN1 for CLC2
    // Required only in devices that do not have RW0 routed through PPS output
    CLCIN1PPS = 0x38;       // 0x38 = RW0 on PIC18F46Q71
    
    // Enable flip-flop on RW0
    PORTWDFbits.DF0 = 1;

    // Select clock
    PORTWCLK = 0x00;        // 0x00 = Fosc on PIC18F46Q71

    // Initialize state machine to a default state
    PORTW = 0x01;           // Locked state (L=1)

    // Enable clock to start state machine
    PORTWCONbits.CLKEN = 1;
}