Hardware manual

Microcomputer Technical Q&A

Q&A No.: QAH8S-056

Category: Pins

Subject: Address Pin States in On-Chip Memory Access

Question

When on-chip ROM or on-chip RAM is accessed, is the on-chip ROM or on-chip RAM address

output off-chip?

Answer

When on-chip ROM, on-chip RAM, or an internal I/O register is accessed, the address bus retains

its previous address value, and the on-chip ROM or on-chip RAM address value is not output off-

chip (see figure below).

This is effective in reducing current dissipation and noise.

Internal

address

External

address

External

memory

On-chip ROM

On-chip RAM

Internal I/O

External memory address held

Address Bus in On-Chip ROM, On-Chip RAM, and Internal I/O Register Access