3v0 said:The CPU is designed to either start fetching/executing instructions from a fixed address, or to load an address from a fixed address and start executing code there.
It is up to the person who designs/programs the system as to what code is at the starting address.
If you have a more specific question I would be happy to provide info.
ArtemisGoldfish said:Alright, another question: Can processors (some, most, any) directly fetch instructions from ROM/RAM, or do they have to be prepared with some logic circuit?
Leftyretro said:Most all fetch their instructions from a ROM/RAM, that is a common feature of any general purpose processor. In reality the processor doesn't know or care what kind of memory is being used when it fetches an instruction, It just places an address onto it's address buss and expects to receive the instructions back on it's data buss, so where the instructions are contained is just a implementation detail for a specific processor.
Lefty
ericgibbs said:hi,
So, in effect, I could take a Parallel EEPROM like this: Datasheet , write the instructions to it in the CPU's set (assuming it's 8-bit also, since the ROM is 8-bits wide) and it'd start executing instructions?
Im afraid not.
The memory only holds the programmed instructions, it dosnt execute them.
The instructions are executed by the CPU.
Eric
ArtemisGoldfish said:So, in effect, I could take a Parallel EEPROM like this: Datasheet , write the instructions to it in the CPU's set (assuming it's 8-bit also, since the ROM is 8-bits wide) and it'd start executing instructions?
3v0 said:Yes, if you mean the CPU starts executing the instructions.
Not sure about the specific device you mentioned. There is a timing issue, put simply the memory needs to have a speed compatible with the processor.
I am curious regarding why you are asking this. You can buy micocontrollers with enough built in flash to do most jobs. Maybe if you let us know where you are going with this we can save a few posts and jump to the end.
Are you interested in knowing how a PC boots ? Or is this confined to microcontrollers ?
ArtemisGoldfish said:Sorry about not really giving any of my intentions. I hope to learn enough to be able to build a simple, old single-board computer, much like the Spectrum Z81 (But without the high price tag and limited availability). I would use microcontrollers, but that really ruins the fun for me, and I'm really into the fun of experimentation.
3v0 said:At one time a friend and I built a SBC Z80 that ran forth. It used 2 SCC chips (4 serial channels), other then that most 16F pics would run rings around it.
3v0 said:Not a problem. I am an old Z80 fan.
At one time a friend and I built a SBC Z80 that ran forth. It used 2 SCC chips (4 serial channels), other then that most 16F pics would run rings around it.
Your biggest problem will be getting a ROM programmed with the proper boot code so you can load code into RAM/EEPROM and execute it. There are ROM emulators out there that are ideal for experimenting with building your own simple computer board:I'm interested in building a simple computer now that I know some of the theory.
Sceadwian said:I have an AVR chip that has an external memory bus interface and it's in DIP, microchip must have at least one?
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