Unusual experiences you have encountered while debugging ?

Started by Simon Clubley May 28, 2015
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 <> wrote: >>> On 5/29/2015 2:29 PM, Simon Clubley wrote: >>>> On 2015-05-29, Don Y <> 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