[Coco] Kip's Single Board Computer

[John W. Linville]

On Mon, Sep 14, 2015 at 09:31:37PM -0400, Kip Koon wrote:

> I apologize for not responding sooner as I have not been doing well.  Once I
> saw and read all the emails and requests to help, thanks guys, here are PDFs
> for the Kipper SBC v1 that Retro Innovations and I have been working on.

I found your earlier post from back in the Spring and took a look at
those schematics this week...
 
> I guess looking at the same schematic for long periods of time is not good
> for finding errors since I could not find any until recently.  Here are the
> few errors I have noticed.
> 
> Looking at sheet 1 of the schematic, I noticed there is no capacitor across
> the reset pushbutton hence no RC circuit to pull the reset pin low.  In the
> next version, I will be using an MC340649 Voltage level Sensor in a TO-92
> package built to properly reset microprocessors and microcontrollers.  

I'm fairly certain that this is your "no clock" problem.  Page 6 of
the datasheet says "During initial power on, The RESET^ line should
be held low until the clock oscillator is fully operational."
The missing RC circuit performs that task.

I have a Simon6809 board here that has the proper RC circuit on the
RESET^ line.  As an experiment, I pulled out a pin of the capacitor
in that circuit, essentially replicating the "no RC on RESET^" circuit
as in your Kipper SBC v1 schematic.  When I did that, the board would
not start-up when powered.  Replacing that capacitor pin connection
made the board run again.

Anyway, I suspect that the "RC on RESET^" bit is all you need to get
the clock running.  I don't think you need the MC340649 bit at all,
but YMMV...

> Second, though I studied the datasheet for the 6809 microprocessor carefully
> to make sure I did not exceed maximum current limits on pins, I probably
> should have put buffers between the cpu signals and the LEDs.  Buffers will
> be included in the next design.  I'm sure there are other improvements that
> could be done as well.  

Buffering would be good, if you really need those LEDs at all.  I doubt
if they are particularly useful, and they probably don't make a great
light show either -- just my $0.02...

> There are numerous notes in the schematic, however, feel free to ask me or
> Jim at Retro Innovations any questions you may have.  
> 
> In the folder Kipper SBC v1 in my dropbox are the schematics and board
> layout with dimensions at the following link.
> 
> < https://www.dropbox.com/sh/lhpa2j2qy78wi1u/AADQENXcZltISTHB_6_IE5oYa?dl=0>
> 
> Everyone is welcome to chime in.  I'm looking forward to our collaboration.
> I'd like to make this first version the best it can be for what it is
> designed to do.  Thank you all in advance for your help.  Take care my
> friends.

Well, good luck -- maybe you will be on the right track now!

John
-- 
John W. Linville		Someday the world will need a hero, and you
linville at tuxdriver.com			might be all we have.  Be ready.