Suppose the microcode ROM is selected as a data source...

Suppose the microcode ROM is selected as a data source during a given clock cycle; that is, $\overline{\mathrm{DR} \mu \mathrm{ROM}}$ is asserted (low) during that cycle. Do the data that appear on the bus during that cycle depend on the value of the ADR+ signal (which increments ADR) during the same cycle? In other words, will the increment signal to the ADR register in the microcode ROM module cause the ADR register contents to increment on the same active clock edge on which the ADR+ is asserted, or does it increment on the next active clock edge?

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Key Concepts

Microcode ROM

Microcode ROM is a read-only memory used to store sequences of microinstructions that control the internal operations of a CPU. It is selected to provide microinstruction data during a control cycle, and its operation is based on synchronization with the processor clock, ensuring that data retrieval and control signal activation occur in a defined temporal sequence.

Clock Edge Timing in Synchronous Digital Systems

In synchronous digital systems, operations are driven by active clock edges. All state changes, such as register updates or signal transitions, occur relative to these edges. This means control signals including increments, data latching, or state updates, are typically designed such that their effects are realized on either the current clock edge or the subsequent one, depending on the design.

Register update timing refers to the moment when registers in a digital circuit, such as the microcode address register, capture new data based on control signals. When an increment signal like ADR+ is asserted, it typically causes the register to update its value on the next active clock edge, ensuring that the data available on the bus during the current cycle is not affected by the pending update.

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