Holdciklus

Holdciklus is a term used in digital electronics to describe a hold cycle, a phase within synchronous bus timing during which certain signals must remain stable to ensure a correct data transfer. In many systems, each clock edge triggers actions on the bus, and data must be set up before the edge and held for a specified interval after it. If a peripheral device requires more time to complete its operation, the controller may insert one or more hold cycles, effectively adding wait states to the cycle.

During a hold cycle, the address and data lines are typically not changed, and the bus remains in a stable state while the slower device completes its task. The need for hold cycles arises from timing margins between fast processors and slower memory or I/O components, and they are a practical mechanism to ensure reliable communication without rushing data.

Hold cycles are governed by timing constraints such as setup time and hold time. Setup time is the interval before the clock edge when data must be stable, while hold time is the interval after the edge during which data must remain stable. By inserting hold cycles, designers can accommodate longer device response times and maintain proper data sampling.

In practice, hold cycles are implemented through bus controllers and memory controllers using ready or acknowledge signals or by inserting wait states in the clock stream. Design considerations include meeting hold times under process, voltage, and temperature variations and defining how many hold cycles may be inserted in a given transaction. The term is often used interchangeably with wait states in some architectures, though terminology can vary by language and vendor.