Re: External KERNAL using a 6510
Date: 2000-08-30 22:01:46

Hallo Spiro,

> There are two reasons why you can't use a simple latch:
> 1. You've got to emulate the behaviour of the DDR at $0000, too.
>    So I has got to be a more sophisticated latch. (I don't know
>    the 373, so I cannot say if it would handle this correctly).

The circuit only uses P1 which is an output after the I/O initialisation. And I 
don't know of any program changing it for any reason. 

> 2. The 6510 handles $0000 and $0001 internally, so read and write
>    access cannot be seen from outside.

That is what I think as well. But if there is nothing to be seen on the 
address- or databus, how does this external 6510 know what to do ??????

>  That's the main reason why a 6510 is used: It always exe-
>    cutes the same opcode and data as the internal 6510, so any store
>    to $0000 or $0001 is the same as internally, so the on-chip port
>    provides the same information as the one of the internal 6510.

What you're saying is that the external 6510 is executing the same program as 
the internal one? I never had thought about that. I thought that it was 
"sleeping" or whatever because its busses had been disabled. 
If the above is the case, then next question: are all produced 6510's the same 
and if not, does that matter in this case?

Groetjes, Ruud

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