[Coco] Grant Searles SBC

[Zippster]

Well, since your clock is right at E, timing should be right for the 68B50.

I agree on putting a cap between reset and ground for an analog debounce on the switch.
You might try 10k & .1uF for values there.

Considering you are getting some output and the clock is right, I’d really scrutinize that FTDI chip and the connections there.
Does it work just going 68B50 —> MAX232 —> Terminal?

- Ed




> On May 6, 2015, at 6:51 PM, Bill Nobel <b_nobel at hotmail.com> wrote:
> 
> BA is goes high and sometime BS is oscillating between High and Low.  I seems the the CPU doesn’t grab the reset vector properly, but I have verified the Eprom byte for byte.
> 
> Now it does’t do this all the time most times power up BA/BS are low until I hit Reset. then things go haywire.  I traced each line 4 times now and I am at a loss as to what I have wrong.  2 thing I changed from Grants circuit is that I am using a HD63C09 and a AS7C256 static ram (same one Kip uses) instead.
> 
> Sometimes the garbage on the terminal is just a continuous stream non stop, and sometimes bursts in packets.
> 
> Bill Nobel
> 
>> On May 6, 2015, at 5:32 PM, Matthew Stock <stock at bexkat.com> wrote:
>> 
>> Bill,
>> 
>> When it's in this state, what do BA and BS look like on rise of Q?  are
>> they both high?  If not, it's not a halt state but something else.  Only
>> thing I can think of is to put a 1uF cap between the reset line and ground
>> to complete the RC circuit and see if that helps.  I suspect the reset
>> isn't a clean slope and that's annoying the CPU.
>> 
>> Matt
>> 
>> 
>> On Wed, May 6, 2015 at 7:16 PM, Bill Nobel <b_nobel at hotmail.com> wrote:
>> 
>>> Hi guys.  This is a shout out to the Hardware Experts out there.  I am
>>> trying to build this unit on a breadboard and am having some issues.  I am
>>> following the circuit to a tee.  Powering up I get 1.843 mhz on the E & Q
>>> lines R/W is working.  But sometimes when I hit reset my BA line goes high
>>> throwing CPU into HALT state even though my HALT is tied High.  Also on the
>>> terminal window I am getting nothing but garbage @ 115200 baud.  The one
>>> difference to the circuit I am using a FTDI instead of the 9 pin serial
>>> plug.  I verified the FTDI by connecting to a old desktop pc using
>>> Hyperterm so the chip is working.  But on the SBC I get nothing.  I even
>>> went to the extent of swapping out all the chips and verified by hand the
>>> Eprom code to see if it Burned properly.
>>> 
>>> Any suggestions or help would be appreciated.
>>> 
>>> Bill Nobel
>>> 
>>> 
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