[Coco] MC6809 Inards
smostrom at mn.rr.com
Tue Oct 3 21:49:41 EDT 2006
Any chance that patents could be reviewed for the hidden graphics modes
for the Coco3?
-- Steve --
jdaggett at gate.net wrote:
>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.
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