THE BOARD
=========
Status: unfinished
Version: 1.0
This MSX3... It's really not that hard to build (ofcourse that's a relative
term). This is what basically has to be done:
When it's finished (or almost finished), take Ademir's ACE002 board, remove
the Z180, insert a Z380 (leave A31-A16 and D7-D0 unconnected, connect the
memory's databus to D15-D8 and keep /MSIZE low), and you've already got a
fully functional mainboard with Z380. All 16/32-bit registers and the
extended instruction set etc. work. However, the 64k address range limit is
still there.
To add linear memory etc. the address and databus have to be extended to
32/16 bits. So, lay a few extra lines on the mainboard -while you're at is,
also replace the slot by a 32-bits one-, connect them with the memory and
put some extra logic inbetween which uses a mapper if the given address is
<64k (A31-A16 == 0).
Now you can enjoy the enhanced address range too!!! There are only a few
more things which have to be changed...
Replace the BIOS-ROM with FlashROM, so that the BIOS can from now on be
changed and updated very easily.
You see, we still can't switch back from 'enhanced' mode to 'legacy' mode,
that will require some extra effort. What has to be done is to give the
engine another register (a single bit will do fine too). After power-up or a
reset this register equals 0. To switch back to 'legacy' mode, a
BIOS-routine is called which saves the desired return-address at a fixed
RAM-location. Next, it writes a 255 to the register in the engine. This
causes the engine to send a reset-signal to the Z380 during 10 busclocks
(however preventing this signal to reach other devices). Then the BIOS
executes its startup sequence in which it tests the engine's register. If
it's nonzero, the processor resumes at the address saved in memory. By the
way, since on reset, most registers stay preserved, the return-address could
as well be passed in a register.
That was it! Now you can enjoy the Z380's full power, with as well old as
dedicated software. Now we can begin improving the BIOS with 32-bit code,
add routines, create little gizmo's like custom startup-logo's and
animations... We can plug in Padial's 32-bits slotexpander and create lots
of cartridges to put in... It will be awesome!!!
Please reply if you have any additions (but mind the CC's! So hit
reply-all...). About the "status" on top of this text, it indicates if it's
ready for use. So if a working scheme/board has been (virtually) created,
then the status will be finished. Maybe that already is the case with the
mapper (I don't know how it's done on the LPE Z380 system).
I trust the Phoenix webpage maintainer to add this text to the page.
The version increases as updates to this text are being made.
~Grauw
--
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email me: [EMAIL PROTECTED] or ICQ: 10196372
visit my homepage at http://grauw.blehq.org/
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