Fetching from program memory?

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Main Question or Discussion Point

Hello ,
I need help , rom memory is memory that store program. we can only read rom memory.

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look this diagram why does we connect both memory. I have read that when we start to read the program memory. we get data from program memory and store into instruction register. In my first diagram.

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how and where to use Instruction register ?

 

[berkeman]

Hello ,
I need help , rom memory is memory that store program. we can only read rom memory.

[/ATTACH]
look this diagram why does we connect both memory. I have read that when we start to read the program memory. we get data from program memory and store into instruction register. In my first diagram.

[/ATTACH]

how and where to use Instruction register ?

You have different CE~ and OE~ signals for the EPROM and RAM memory chips. They are not both enabled at the same time. You would start with the program reading from ROM address 0x0000 or 0x0001 (depending on the processor architecture), and executing the instructions that you read from there. As the program progresses, it can use part of the RAM memory chip. You would typically have a "memory map" that defines what part of that 64KB ROM and what part of the 64KB RAM you access. You would not generally use all of either chip, since they generally share the same "memory map". Make sense?