HP-21MX bootstrapping?

J. David Bryan jdbryan at acm.org
Thu Feb 21 16:59:15 CST 2008

On 21 Feb 2008 at 12:44, Tim Riker wrote:

> Agreed. The question is why. :)

The microcode sets overflow on at the start of the loader routine and turns 
it off after verifying the starting memory location and the select code.  
These are only these two jumps out of the routine with overflow set.

If P is set as expected by IBL (i.e., 077700 for 32K), then the select code 
>= 10 check is failing.  Perhaps the ribbon cable from the front panel to 
the CPU is bad.

If P is set to 177700 (bit 15 on), then the memory check is failing.

> FYI: I'm started taking notes here:
> http://rikers.org/wiki/HardwareNotes

Your list shows slot 118 open.  The HP installation manual recommends that 
the memory controller go in 118 and the memory cards follow above in the 

You might try reseating the ribbon cable that connects the left-side edge 
connectors of the memory cards and the controller card.  (The right side 
connectors are open.)  Also, the ribbon cable that attaches to the DCPC 

Note that the memory controller must be strapped for an M-Series; if it's 
strapped for an E-Series, the timing will be off.

                                      -- Dave

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