More Bringing up a CPM

From: Allison J Parent <allisonp_at_world.std.com>
Date: Tue Jun 1 21:58:50 1999

<correctly. Hence, DRAMs before '83-84 were somewhat iffy on the S-100. B
<then, of course, the S-100 was, more or less, history. One of the things

There were a few that worked really well but one look at the design said
why, good designs work. One of the worst ones used gate delays for the
ras-muc-cas timing...

<may be, but DRAMs are not as difficult or fussy as a lot of people have
<said. I've designed literally dozens of different DRAM circuits which in

The ones that work were near unbreakable, there wer a few notables by 1980
and by 82 a swamp of them.

<DMA was popular for early FDC's in the mid '70's because 8080 processors
<were too slow to get around the loop fast enough to transfer data from

Not true for S100 systems. DMA was hardware intensive and the 8257 was
too expensive and too difficult to use with the rather helter skelter
signals. The 8080 would do SD 8" no problem and DD5.25 with not much
difficulty but the programming tricks were basically ugly.

CP/M only moved 128 bytes at a time, so moving multiple sectors was wasted
for the most part unless you were caching.

In the multibus and STD bus worlds things were quite a bit saner.

Allison
Received on Tue Jun 01 1999 - 21:58:50 BST

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:32:15 BST