Last night was looking at 30070-90009_S33_schem_Jan79.pdf and thinking it would be good to have a System Reference Manual and microcode listing and description for the Series 30/33, you would also probably find it helpful for understanding the microcoded test routines too.

The closest approximation to a how-it-works that is easily available on the Internet today is probably the July 1979 HP Journal.  The PCU, RASS, and RALU chips basically are the micromachine, running code from a 32-bit-wide microcode ROM array.  RASS is kind of interesting in that it does (among other things) address bounds checking in hardware.  On SIO 3000s I think it is done in microcode.

-Frank McConnell

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