Unknown S100 system - test-drb@ccmp.vtda.org

23 Sep 2007

...

Subject: Re: Unknown S100 system
   From: "Roy J. Tellason" <rtellason at verizon.net>
   Date: Sun, 23 Sep 2007 12:56:42 -0400
     To: cctech at classiccmp.org

On Saturday 22 September 2007 08:29, Allison wrote:
  With
regard to what little programming I've done,  the thing I like most
 about the z80 is relative jumps,  which makes relocatable code easy to
 do.  The other big deal is the alternate register set and the index
 registers,  which I really haven't used all that much. 
 The items that make z80 desireable for programming to me are the repeat
 instructions (LDIR) and the loop (DJNZ)  
Aside from making source a bit more compact,  those seemed to,  like a lot of 
other stuff,  require the use of particular registers,  etc. that I might 
have other uses for at the time.  And didn't seem to offer that much of a 
speed advantage.  I never got into them all that much. 
They made the source easier to read as well.  As to use of registers
for block moves in 8080 your likely to use the same set and the same way 
so no biggie. In balance I like Z80 and it does add some nice expansions.

...
   plus some of
the smaller instructions that make the CPU more symetrical.  It
 always bugged me that 8080 can load the SP but storing it required clearing
 the HL and adding SP to HL. 
Yes!  It also bugged me that you could swap HL and DE easily enough,  but not 
HL and BC,  or DE and BC.  That being a single-byte instruction that executed 
fairly quickly,  as I recall... 
Yep, 8080 was very lopsided but I'd guess leaving out some fo the instructions 
simplified matters back when it meant something.

...
   8088/86,
hardware around it was easy, hated programming it.  Always felt
 it was an 8080 with a bag on the side and borrowed the worst z80 features.
 It's big cache was it's was 16bit and had the ability to address 1mb. 
That approach to things struck me as an abomination the first time I looked at 
it,  and I never really got all that interested in doing much of anything 
with it at the assembler level -- if I need to program something that has one 
of those in it I'll do it in c or whatever,  so I don't have to be bothered 
with all those messy details.  It's unfortunate that this is the chip family 
that the industry seems to have settled on,  mostly. 
Any 808x or 80x86 I program in high enough level language as to totally 
obscure the crap underneath. Lowest being database stuff like SQL or maybe 
Pascal.  PC hardware I code for only when people are paying.

...
 I feel the same way about a lot of the intel-type (and
similar) peripheral 
chips -- write-only registers?  WTH?  I suppose that some aspect or other of 
chip design pushed things in that direction,  but looking at it from just the 
perspective of programming the things,  I don't see where I/O address space 
was all that scarce a resource,  really. 
Write only makes sense when you consider it saves addreses and logic in there
and likely most will never read it.  Some the write is one register and read
is another but they share a common address.  All in all I've seen better and 
worse.

Allison