I will try and get hold of a logic probe from ebay :)
On Friday, 12 April 2013 09:10:09 UTC+1, douglas_goodall wrote:
>
> Sam,
>
> Here is a snippet from my previous posting to a fellow debugging an SBC.
>
> It might help you...
>
> Douglas
>
> Using a logic probe to debug sbc
> Page history<http://n8vem-sbc.pbworks.com/w/page-revisions/62743544/Using%20a%20logic%20probe%20to%20debug%20sbc>last
> edited by Douglas W. Goodall<http://n8vem-sbc.pbworks.com/w/page/62743544/Using%20a%20logic%20probe%20to%20debug%20sbc>
> 2 months, 3 weeks ago [image: Saved with comment]<http://n8vem-sbc.pbworks.com/w/page-revisions/62743544/Using%20a%20logic%20probe%20to%20debug%20sbc>
> I would like to share a little with you about how a logic probe can be
> used to debug your sbc.
>
> First off the probe must be connected to +5 and Ground. If a board is
> problematic, I solder
> a pin of some kind at a power and a ground point for the probe.
>
> The probe most likely has what is called a pulse stretcher. The pulse
> stretcher takes an event
> that happens very quickly, and turns it into a long enough flash of the
> LED on the probe, so that
> a human can see the LED change state.
>
> The first thing I usually test for is the clock input to the Z80. It
> should be changing state a
> million times a second or more, so the probe should be blinking when you
> look at that signal at the Z80.
> IF it is not blinking, then go back to the crystal oscillator and make
> sure it's output is blinking. If the
> oscillator is wiggling, but the clock input to the Z80 is not. Do a
> continuity verify between the oscillator
> output and the clock input on the Z80 (with the power off of course). If
> there is no connection between
> the oscillator output and the Z80 clock input, you are either looking at a
> trace problem on the board, or
> you counted wrong on the Z80 pins. If you are sure of your pins and no
> continuity, you may have a
> socket problem. Check the continuity between the Z80 clock input pin, and
> the solder pad on the
> back where that socket pin comes through. If you have the signal on the
> backside pad, but not on the
> chip pin in the socket, you either have a bad solder jointwher the socket
> pin goes through the board
> or you may have a bent under pin on the clock lead of the Z80.
>
> Now that you are sure the Z80 has it's heartbeat, the next question I
> would ask, "Is the Z80
> executing code? Use the logic probe to check the chip enable line of the
> ROM/FLASH to see
> if the CPU is addressing the RAM.
>
> Next I would look at the chip select on the UART to see if the code is
> sending it initialization bytes.
> If the chip select is not wiggling, check to see if the output of the I/O
> address decoder is wiggling the
> line which goes to the UART chip select. If it is not, there may be a
> problem in the I/O decoding logic.
>
> This is my logical approach to debugging the board. I have not written the
> complete procedure for
> debugging the entire board, but have given you a little of the kinds of
> things you might be considering
> while you have the logic probe in your hand.
>
> Chances are if you approach the board this way, you will know soon which
> subsystems are working
> and where the chain of logic breaks down .
>
> On Apr 11, 2013, at 3:48 PM, Samuel Castledine <samuel.c...-***@public.gmane.org<javascript:>>
> wrote:
>
> Hi,
>
> I've been trying to get my Zeta up and running however I've run into some
> problems.
>
> Current setup : no PPP, using standard ROM, no jumpers set. Using USB to
> RS232 cable.
>
> When connected to the PC nothing is received in the virtual terminal
> (using HyperTerminal, 38400,8,none,1,none). At first I thought it
> was the cable however after testing pins and doing a loop back test
> it doesn't seem as though its that.
>
> Here is some pictures of the board:
> Bottom :
> https://www.dropbox.com/s/e9ixagkd4f5pfaw/2013-04-10%2021.05.55.jpg
> Top : https://www.dropbox.com/s/pmo5vuk83ve287o/2013-04-10%2021.04.31.jpg
>
> I've also attached a detailed parts list with links to the parts I used.
>
> Many thanks
>
> Sam
>
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>
> <ZetaBOM.xlsx>
>
>
> ---http://www.linkedin.com/in/douglasgoodall
>
>
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