Quote:
Originally Posted by Slothie
Quote:
Originally Posted by ScottishColin
And while I'm waiting for the EPROM, is it possible for someone to either explain to me how the code on the EPROM is called at boot? or is there a website I should go look at?
I'm interested in how the code is called in the first place.
Colin.
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The EPROM is mapped into memory from addresses F800-FFFF. When a 6502 processor is reset, it looks in locations FFFC and FFFD for the address of the boot code. The EPROM has these locations programmed to the start of the diagnostics at F800! The original kernal ROM obviously had different code locations and therefore values in FFFC & FFFD but the principle is the same. |
And just to complicate matters, the original (Not always socketed) Kernal ROM jumps to the (Country-specific, usually socketed) Edit ROM at $E000, after a small amount of processing (i.e. maskable interrupts have been inhibited and the decimal arithmetic flag cleared).
So the Daver2 diagnostic, that replaces the EDIT ROM, boots slightly-differently and needs the proper (& working!) Kernal ROM fitted.