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Codiode/Problems/Sequential Logic

SPI Mode 3 Timing

MediumLogic CircuitBuild

High-speed peripheral interfaces rely on precise clock polarity and phase configurations to synchronize data transfers. SPI Mode 3 provides a robust timing scheme where the clock line remains high during idle states.

Construct a circuit that generates the sck and mosi signals for an SPI Mode 3 interface. The system provides a free-running clk, an active-high en signal, and the next bit to transmit on tx_data.

The sck output is purely combinational and must follow this exact behavior based on the system clock and enable state:

| clk | en | sck | |-------|------|-------| | 0 | 0 | 1 | | 1 | 0 | 1 | | 0 | 1 | 1 | | 1 | 1 | 0 |

The mosi output must capture and output tx_data exactly on the falling edge of sck. Assume mosi initializes to 0.

Constraints

  • Implement sck using only combinational logic.
  • Use exactly one D-Flip-Flop to drive the mosi output.
  • Do not use asynchronous reset pins on the flip-flop.

Topics

TimingSPICommunication

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