At 16:43 03/10/98 +0200, you wrote:
>At 04:14 AM 9/13/98 +0200, you wrote:
>
>>Question: In linear address space mode, is it still Z80 (MSX)
>>compatible?
>
>>From Zilog Z380 user's manual, chapter 3:
>
>The Z380 has a native and an extended mode.
>
>In native mode the Z380 is compatible with the Z80. It can only execute
>code in the first 64K of memory. Using a trick you can access data anywhere
>in memory, but in the default configuration this is also restricted to the
>first 64K.
Not 100% true, even in native mode the Z380 ALU still 32 bits and by the
way some coding tricks like:
imagine you have to countdown the time of a game or what ever you want
LD DE,(TimeCounter)
LD HL,-2
ADD HL,DE
this wont give the good result on Z380
If you code it the right way:
AND A ;clear CARRY
LD DE,(TimeCounter)
LD HL,2
SBC HL,DE
Then you'll get the right answer.
Explanation:
in the first exemple, -2 is FFFEh in 16 bits size but in 32bits size it
should be FFFFFFFEh !
Now imagine that the value of TimeCounter is 2 (0002h in 16 bits), if you
add both HL and DE:
0002 content of TimeCounter
+ FFFE -2 to be add
-----------
10000 32 bits sized result
0000 16 bits sized result
Ok, if we just look at the first 16 bits the result is the same but in
16bits sized ALU the Z flag will be set but not in 32 bits ALU
Think the same way for the next example, imagine you have a counter that
count from 0 to 65535 (FFFFh) if it is FFFFh and you increment it then it
goes to 0000h and set Z and C flags of Z80, but in Z380 it will simply
gives: 10000h with out Z and C!
Their will be a big task for people who gona code the System ROM....
BTW I've never used the ADD with -2 tricks in my onw code, but I know that
some did. So compatibility is not garanted if we do not take care of this
kind of problem.
I'm not really interested in an MSX380 100% compatible with MSX, if I want
ot play MSX game or demos, I still have my MSX Turbo R or an MSX2. I think
that the "new" MSX should free the power of the Z380 and other hardware to
get a realy stong machine, the project paper sheet I've seen in Tilburg was
very interesting, it was planing to use an enchanced version of the SNES
(super FAMICOM) VDP for the video, I really prefer the the system is
desinged to operate in 32bits to boost disk and memory access, using fast
SRAM or maybe SDRAM.
greetings and good luck for the project
Martial.
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