Olivetti M20 - test-drb@ccmp.vtda.org

14 Jan 2007

Can anyone please tell me if the Olivetti M20 used a Z8010 memory  
management unit?

When I worked for Marconi Elliott Avionics at Rochester we designed  
the anti submarine
sub system for the WG34 (Later EH101) helicopter using a dozen Z8001s  
and Z8010s
plus lots of specialised processors. After I left the company, the  
project dragged on for
many years before being cancelled and a rival, more mainstream system  
fitted.

The Z8001 had 16 low order address lines and 7 segment selector  
lines, so even
without an MMU, it should have an 8MB address range. IIRC, the MMU  
took the
top 9 address lines and the 7 segment selector lines and could map  
them onto
a 16MB address range. For speed and simplicity, I came up with the  
idea of never
setting the bottom bit in the segment base registers so we could send  
the bottom
8 bits of the CPU address directly as the row address to the RAM  
chips and
by the time they were ready for the column address, the MMU look-up  
was done.
Hence we allocated memory in 256 byte chunks instead of 128 bytes as  
envisaged
by Zilog.

In the M20 uses a Z8010 I might get one if one comes up for sale in  
Europe.

Roger Holmes

On 10 Jan, 2007, at 16:36, cctalk-request at classiccmp.org wrote:

...
  Message: 8
 Date: Tue, 09 Jan 2007 22:49:27 -0800
 From: "dwight elvey" <dkelvey at hotmail.com>
 Subject: Re: Olivetti M20
 To: cctalk at classiccmp.org
 Message-ID: <BAY130-F3347994A26286E3E09D04DA3B20 at phx.gbl>
 Content-Type: text/plain; format=flowed

  From: Gene Buckle <geneb at simpits.com>

 dwight elvey wrote:
  Hi
 For those that might be interested in an Olivetti M20, there is one
 on eBay. This was one of the few machines made with a Z8000  
 processor.
 I think the only personal computer.
 If someone on this list gets one, contact me and I'll help you get
 it up and running.
 Dwight 
 That's cool.  I just posted PDFs of the CP/M for Z8000 manuals on the
 Retroarchive site. :)

 g.

 Hi Gene
 I would suspect that the one on eBay isn't ready for CP/M8000 right
 out of the box. I'm sure it'll handle PCOS, at least version 2.0f.
 The problem is that most machines didn't come with enough memory
 for CP/M8000. Although, the manual for CP/M8000 states that one
 can run in a machine with 128K of memory, because of a number
 of allocation issues in the M20, you really need 384K.
 The M20's comes with 128K on the mother board and usually
 have two 32K expansion memory cards. Even with three of these
 32K cards, your only up to 224K. Still not enough.
 When I first got CP/M8000 running on my machine, I modified
 two of my memory cards to take 64K DRAM chips. This brings it
 to 384K. I was always going to increase it to 512K, the most that
 the M20 decodes, but I don't see the need any more.
 A fellow in Italy had thought that it might be easier to take two
 1 meg simm's and use those ( you need at least 2 because it
 does access 8 bit or 16 bit and needs the separate selects ).
 We talked it over and came up with a way to wire them up
 such that they can provide 384K with a minimum of external
 hardware( total of 512K with the mother boards memory).
 The only painful issue is that the M20 normally has a select for
 either 32K or 128K at each board position. The first solution
 used three board edges to connect the two other connectors
 selects. Another fellow built one that he made a header to
 go under the NAND gate chip that normally sent out the
 selects. This did require lifting one part and putting it on a socket.
 It also seems that some of the memory boards came with sockets
 and could be configured for either 32K or 128K by jumpers
 but none of my board were that easy. 