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Workbench Notes

My full time job is keeping me very busy, but there is still some time during the week to squeeze in some Corsham Tech fun.  This post isn’t about any one thing, so bear with me.

Over the years I’ve accumulated a number of oscilloscopes, always used, usually from hamfests, computer shows or friends’ basements.  Yes, I do like the old Tektronix scopes, but after using modern scopes at work for many years, I finally decided to break down and buy a new Rigol scope.  I’m 55 years old and finally bought a new scope!  It was very handy the last few days debugging a new version of the SS-50 motherboard (more on this later).  Frequency counter, I2C decoder, and four channels… I should have done this a long time ago!

For those of you who with our SS-50 systems, we’ve been through a lot of revisions of the motherboard.  Version 1, 2, 3, 4, then 4A.  As each was finished it seemed like a perfect product until either a small bug was found or a new feature was needed, like when it was modified to support both 6800 and 6809 processors.  Rev 5 is the latest and fixes all known problems and does everything it needs to do.  It’s still going through additional testing but does support 6800 and 6809 CPUs.  The only big remaining test involves NitrOS/9 interrupt support.  This was the problem with the rev 4 motherboard.

During testing, it worked fine for the 6800 but gave very unpredictable results for the 6809.  Hours were spent reviewing the schematic but nothing seemed wrong.  Fortunately I had a new scope to work with, so after some debugging it came down to one IC not being quite fast enough for some of the decoding.  The scope showed it was plenty fast for the 1 MHz 6800 but a bit slow for the 2 MHz 6809 and the tighter timing.  One chip was tossed into the trash, a new one taken from tube, and the motherboard sprang to like and has been running memory tests non-stop for over 50 hours.

Most of my software work recently has been on the 6502, including writing a Tiny BASIC from scratch, and bringing up fig-FORTH on the KIM Clone.  I also want a better 6502 debugger and have been spending a bit of time on that.  I am technically a software engineer and only dabble in hardware so I have something to write code on.

Oh well, the soldering iron is hot, so it’s time to get back to the workbench…

Bob

 

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KIM Clone is Available!

After many months, it’s finally available… in small quantities!  This takes a lot of time to build, and takes a lot of parts that are being ordered, so I’ll probably only be able to build/ship one or two units per week.

Assembled units are available in the shopping area.  These are initially using the rev 1B boards which are fully functional but have some silkscreen errors.  Ie, some of the text printed on the surface is not correct; this has nothing to do with functionality.  I stopped doing serial numbers years ago but have decided to start again.  This is board #3:

The keypad has nice buttons that click when pressed.  Getting custom printed keycaps was out of my price range, so these are standard caps with white/clear printed labels on top.  Getting those buttons labeled is the single most time consuming process to build a board.

The USB interface to the PC is along the top.  Earlier I mentioned silk screen errors, and here is one of them.  Below our URL should be “Version 1B” but it was put on the back side of the circuit board by mistake.