17 Dec
2018
17 Dec
'18
11 a.m.
On Dec 17, 2018, at 10:52 AM, Noel Chiappa via cctalk
<cctalk at classiccmp.org> wrote:
But it does *no* harm if the underlying memory does *not* have a destructive
read-out. Otherwise all of those (even DEC branded) MOS memory boards
wouldn?t work. ;-)
The DATIP and friends were an optimization implemented in the bus protocol
to allow for it to take advantage of the behavior of core. However, nothing
breaks if the memory doesn?t implement a destructive read-out.
TTFN - Guy
From: Paul Koning
For that matter, core memory details such as
destructive read weren't
visible to the CPU
Umm, not quite. If you'd said 'core memory details such as destructive read
weren't visible to the _program_', you'd have been 100% correct.
But as I suspect you know, just overlooked, most (all?) of the -11 CPU's do
use 'read-modify-write' cycles on the bus (DATIP in UNIBUS terms, DATIO in
QBUS) where possible precisely for the benefit of core memory with its
destructive readout. (And there's some hair for interlocking the multiple
CPU's on the -11/74 which I don't recall off the top of my head.)
And I have a vague memory of something similar on other early DEC machines;
probably some -8 models.