Unusual experiences you have encountered while debugging ?

On 5/30/2015 12:20 PM, Don Y wrote:
> On 5/30/2015 8:40 AM, Simon Clubley wrote:
>> On 2015-05-29, Don Y <this@is.not.me.com> wrote:
>>> On 5/29/2015 2:29 PM, Simon Clubley wrote:
>>>> On 2015-05-29, Don Y <this@is.not.me.com> wrote:
>>>>>
>>>>> The "normal" application was obviously too long to bit-switch in
>>>>> like this.
>>>>> A tiny bipolar ROM (I think 16x16 -- or maybe 32x16?) did the normal
>>>>> bootstrap... which loaded the image from a "data cassette" (the
>>>>> "Compact Cassette" format that was popular for music, at the time).
>>>>> Once loaded (into *core*), it was persistent, of course.  So,
>>>>> subsequent
>>>>> power-ups just caused the code to start running immediately
>>>>> (cassette load
>>>>> was pretty slow).
>>>>
>>>> Ok Don, you are now making me feel old - I've also done the load
>>>> programs
>>>> from cassette routine. :-)
>>>
>>>   From *data* cassettes?  Or, from *audio* cassettes (Kansas City
>>> Standard)?
>
>> Good point. :-) The Compact Cassettes in question were sold as audio
>> cassettes.
>
> I suspected.  These were special data cassettes.  IIRC, a clock track
> was prerecorded on the media.  The tapes would go bad frequently.

I worked on a design once to pull data from a tape like this.  It had a 
clock track which was solely to control the tape movement and the data 
was Manchester encoded.  The company I worked for "inherited" the design 
from someone (perhaps a government facility) who wanted it to be sold 
commercially.  The design wasn't bad, but they forgot a few things that 
you just don't do in production like leave TTL inputs floating.  It 
would have very intermittent errors from a FF being reset randomly (open 
reset input).  That took a while to figure out.

I remember learning about CMOS being sensitive to static discharge.  I 
don't recall how I picked up a charge, but I zapped a board of mixed TTL 
and CMOS.  When I debugged it I found that nearly every CMOS chip was 
zapped while the TTL was all good.  This was *long* before anyone was 
wearing wrist straps for static control.

-- 

Rick