PDP-11/45 RSTS/E boot problem

Jerry Weiss jsw at ieee.org
Mon Feb 11 14:22:31 CST 2019

On 2/11/19 12:31 PM, Noel Chiappa via cctalk wrote:
>      > From: Jerry Weiss
>      > Though not a disk controller, the DEC DR11-B/DA11-B would not cross 64K
>      > boundaries.
> Interesting! What's odd is that the DR11-B uses the Bus Interface card (M7219)
> from the RC11 controller, and that _can_ cross moby boundaries, so clearly it
> has the right overflow output; someone just decided not to implement it - the
> DR11-B sets ERROR instead on an address overflow. Wierd.
     Yes the overflow sets error and halts the transfer.  There are 
registers for the extended bits in the DR11B, just missing a few gates 
to increment.   My recollection is that my simple mod wouldn't allow the 
read back of the incremented extended bits, but in my use case this was 
never a problem.

> Anyway, it will be interesting to see if RSTS operates correctly once this
> problem is fixed...
> 	Noel
Yes if turns out the increment was not functional for one or both 
extended address bits, it is impressive that UNIX booted successfully 
without tripping over a boundary.


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