S.Elliott's blog

Side-by-side graphics/text windows

This blogpost is a partial-transcript of a discussion from Apple2Infinitum on Slack, which was spawned from an even older Facebook thread.  Since it isn't easy to view the old discussions on Slack and Facebook, I've copy-pasted the messages, pictures, and code blocks below...

 

Scott Elliott Sep 3rd 11:29:17 AM

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Nibble Histogram: the seeds of a disk-o-scope

What is the distribution of raw nibble values of the bitstream a Disk ][ controller would read from an ordinary DOS diskette?

What values would arise from a copy-protected game disk?  Or from a .DSK emulation of a diskette?

This little routine captures incoming nibbles and computes a moving-window histogram of their distribution.  The data usually stablizes after about 8 calls because it applies a base-2 logarithmic decay to the values after each iteration.

EPROM data rot in my EPROM programmer's EPROM

I recently discovered that some of my custom EPROMS from the 80's and 90's are exhibiting problems due to EPROM bit rot, which falls under the general category of data degredation...or 'data rot'.  Bit rot causes any programmed 0 bits to revert back to 1 bits, their un-programmed state.  The chip isn't actually harmed, it just loses its prorgamming. 

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