[Coco] Grant Searles SBC

Bill Nobel b_nobel at hotmail.com
Wed May 6 19:51:17 EDT 2015

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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