[Coco] MC6809 Inards

[Steve Ostrom]

Any chance that patents could be reviewed for the hidden graphics modes 
for the Coco3?

-- Steve --


jdaggett at gate.net wrote:

>All
>
>My what you can find out when you start reading patents. I was searching the US patent 
>records for anything that might be related to the MC6809 and actually found about four or 
>five patents that could be directly related to the processor. There is no one single patent that 
>is, in whole, a complete description of the processor. Instead there are several patents when 
>combined, give insight to the internal workings of the microprocessor. I even found several 
>patents regarding the MC6820/21 PIA chip. 
>
>Some interesting things that I have found:
>
>1) The MC6809 and the MC6801/3 are probably more closer related internally than the 
>MC6809 is to the MC6800. An interesting thing is the main CPU processor core schematic 
>for the MC6801 is included in patent # 4266270, Microprocessor having dual internal data 
>busses. Beware this is a huge schematic if you want to print it out. It prints out to about 28 
>letter size pages. 
>
>2) It appears that there are three internal clocks in the MC6809/01/03 and maybe even the 
>MC6811/HC11.The clock system in the MC6801 patent (4266270) has three clocks. I have 
>verified that t here are indeed three clocks running through the schematic. 
>
>3) the address bus internally is split into two separate busses, A0 -A7 and A8 to A15. Also 
>As the title to patent 4266270 suggests there are two seaprate 8 bit data busses in the 
>MC6801/3 processor. When I pulled patent 4200912 and looked at the figures #1 and #2 my 
>eyes nearly popped out of my sockets. Here it was nearly indentical to the MC6809. Low 
>and behold t his patent depicts a MC6809 like processor with two internal 8 bit data busses 
>that has a switch to make the two a single 8 bit buss. The main scope of patent 4200912 
>was a processor having multile IRQ processors. The embodied processor has the IRQ and 
>FIRQ inputs. The registers include the USP,  Y pointer register, and the Direct Page 
>Register. Plus a few others. 
>
>I have started writing a blurb on this and hope to put it up on my webpage soon. This was 
>neat stuff and by pouring through about ten to 15 patents,I came away with a greater 
>understanding of what thought processes went through during the design of the MC6809. 
>Also a greater  understanding of several of Motorola's processors and how they function 
>internally. One t hing that I do understand better is how fast the processor can be clocked. 
>Best I could figure is about 6 MHz and that is pushingit real hard. Three MHz is most likely 
>the max for most parts. To many levels of logic gates to ripple through to get much faster. 
>
>more later
>
>james 
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