[Coco] Interesting reading

[Stephen Adolph]

Great research, but I thought I would mention that a patent does not
necessarily mean it is implemented.  Regardless, an interesting way to
dig up info, never thought of that.

..Steve

On Sat, Jun 19, 2010 at 8:34 PM,  <jdaggett at gate.net> wrote:
> A while back I was doing some patent searches and came across several Motorola Patents
> on the 6800 series processors. I also came across two other patents that covered the FIRQ
> function.
>
> Well today I really started in depth reading of one patent. Well needless to say it is been very
> educational. Figure #7 of the design and the corresponding description of it is enlightening on
> how the hardware inputs work. From everything I read the embodiement processor for the
> invention is the MC6809. No other processor of that time had Reset, Halt, NMI, FIRQ and
> IRQ external hardware inputs. Patent US-4200912, Processor Interrupt System, describes
> much of the logic behind the MC6809 interrupt system and how it works.
>
> I have gathered this from the patent. There is a priority assigned to the external inputs. They
> are as follows:
>
> RESET   1 (highest)
> HALT       2
> NMI        3
> FIRQ      4
> IRQ        5  (lowest)
>
> Also the priority circuit allows for an asychronous reset to occur and if in HALT mode, once
> the HALT input is released a RESET occurs.
>
> So far I have gained even a better insight on the vernable old processor. All this started
> recently because I wanted a cycle accurate 6809/6309 processor for a project I have. I also
> want to put it in an FPGA for increased speed and lower voltage operation. Hopefully battery
> operation capable.
>
> This has been very educational and fun read. I still need to decipher more.  Also if figure #2 is
> correct in the patent, then the 6809 has two 8 bit data buses along with the two  8 bit address
> buses. That would explain a lot of how movement of data could be done without a huge
> amount of buss switches or multiplexors.
>
> Now I have a better idea on how to code the HDL and hopefully a cycle accurate processor
> can come out of it. Eventually a 6309 capability also. I think I am about to move this project
> up the priority ladder now. ( no pun intended)
>
> more as I get further along.
>
> james
>
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