S.Elliott's blog

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. 

A very effective Applesoft memory test

Here's a simple-but-effective Applesoft program that rigorously tests main memory.

In its first pass, the program uses Applesoft's pseudorandom number generator to fill addresses 4096 through 49151 ($1000 to $BFFF).

In its second pass, it resets the pseudorandom number generator and computes the same sequence again...but this time it compares the values that were previously stored in memory and detects any that don't match.


Subscribe to RSS - S.Elliott's blog