Minimal CP-M SBC design - test-drb@ccmp.vtda.org

9 May 2008

...
  Date: Thu, 08 May 2008 07:50:46 -0400
 From: Allison  
...
  I can make the boot process easier as you can plop the
rom in
 mappable space.   The usual arguement is can you get a Z180
 in a package most people are willing to deal with (64pin dip)? 
I wouldn't want to deal with the DIP as it's a "skinny" DIP with
0.050 pin spacing, unlike, say, the 68K.  While it probably makes
little difference on a PCB, it requires an adapter if you're
prototyping--and sockets are hard to find.  It's easier to use the 68
pin PLCC to keep the spacing--smaller footprint too.
...
  The latter is the shadow rom many have refered to.  I
usualy do that.
 And make the rom BIG so not only can I map it in when I want but also
 access part of it  (ROMDRIVE). 
I believe the Amstrad Joyce uses the printer controller to force the
necessary boot code onto the Z80 bus.  (Tony?)  At least I've never
seen a boot ROM on a Joyce PCB.
...
  There is no requriement to boot the system from
"disk"
 and making that change can make bring up simpler. 
But that's where the "authentic" aspect fails me.   Why run a
"vintage" CP/M system without the experience a disk drive gives you?
You'll be deprived of the "BDOS Err on B:" messages.  What fun is
that?
One might as well run an emulation program on a PeeCee.  I wouldn't
be at all surpised to find that someone's done it for the iPod Touch--
there already exists a NEC 9801 emulator for that platform.
...
  Deblocking is not too mysterious.  The real missing
bit in the
 Alteraion guide is how the BDOS telegraphs the need to preread
 and when to skip it.   
Page 14, section 12 entitled "Sector Blocking and Deblocking" in the
Alteration Guide covers it pretty well.  I remember being relieved to
find the information after I struggled with 1.4 not having any such
mechanism.  I don't think it was in 2.0 either, but I can check if
anyone's curious.
Cheers,
Chuck