The Spectrum SE
Andrew Owen speaks for Subliminal Extacy about one of the most
ambitious projects to hit the Speccy
- What is the Spectrum SE?
I am aiming to build a modern Z80 based computer. I expect it to
be used for everything modern x86 and PPC computers are used for
because it will be powerful enough to do it but cheap enough for
people in even the poorest parts of the world to be able to
afford.
- Why have you chosen to base it on the Spectrum?
I got my first Spectrum in 1984. It was a Spectrum +. The manual
was crap so I taught myself BASIC by refering to the commands on
the keyboard (at last a reason for that layout). When I moved on
to an Atari ST I found it much harder to create my own programs
and I missed that about the Spectrum.
When I got Gunter Woigk's Mac Spectacle in about 1995 (the early
version with no sound support, let alone 128K) I started writing
my own software again. So, to answer your question, it is
impossible for the average user to sit down and write a program
in one go for modern operating systems. They are simply too
complicated. I thought, given the number of articles posted on
CSS, there was a real demand for a new Spectrum for precisely
this reason.
- What are the major features?
Well, you have to think of it as a new computer that just
happens to be able to run Spectrum software really, a bit like
the Peters Sprinter only better.
The CPU is a Z84C00 at 21.2814 Mhz. This can be stepped down to
3.5469 Mhz for the purposes of 100% accurate 128 mode execution
(although there isn't actually a 128 mode). It will be possible
to change the processor speed from software or via a turbo
button. The software switch will be compatible with the Scorpion
if possible.
The finished machine will be able to access between 1бМВ and
32MB (not yet determined). The paging system still has to be
sorted out because of trying to maintain compatibility with
expanded Pentagons and Scorpions. Port 7FFD will behave exactly
like a 128 (with D6 and D7 reserved for future expansion). The
first four bits of port 1FFD (D0-D3) will act like the +3 (in
order to support PLUSЗDOS software). The remainder will be as
compatible with the expanded Scorpion and Pentagon as possible.
The ULA will be replaced with a microcontroller in order to
display the screens at full speed. Standard Spectrum and TS2068
modes will be supported with the addition of palettes. The
FLASH/BRIGHT bits of the attribute map will be used to specify a
CLUT of 8 colours for a maximum of 32 colours on screen in the
standard Spectrum mode without palette switching.
There will be two YM2203s in place of the AY chip. They are
register compatible so existing AY stuff will work but they are
more powerful and using two together full digital sound should
be possible. I haven't decided what to do about covox support
since I can't get any decent info on it but if I do I may end up
emulating it via the two YM2203s. There will also be a GM-MIDI
chip and a DAC. The output will be a 16-bit stereo signal at
ЧЧKhz.
The keyboard and mouse may be PS/2, PSX or USB depending on what
works out cheapest. There will be at least one serial port
capable of using a 56K modem (for internet connection). There
will also be a parallel port. Both these will be driven via
dedicated hardware. There may also be support for Playstation
game controllers and memory cards (128K capacity).
The first four ROMs are mapped in using the +3 paging system.
There may be a fifth ROM is paged in externally using the ROM-CS
line in order to support TR-DOS.
ROM 0 contains the BIOS. This performs any system tests and
intialises the machine before passing control on to ROM 1
(BASIC). The advantage of this is that the RST 0 instruction can
now be used from ROM 1 to provide up to 65536 system commands.
ROM 1 contains a version of BASIC derived from the original 48K
machine. However, BASIC extensions are stored in ROM 0 and
called on the fly from ROM 1.
ROM 2 contains the primary disk system of the SE; PLUSЗDOS. This
provides support for the majority of +3 applications and allows
+3, CP/M, and CPC disks to be read. The ROM also contains IDEDOS
which allows the use of a hard disk. ROM 3 is empty at the
moment but will probably end up containing a
monitor/assembler/disassembler and snapshot tool while ROM 4
will eventually contain a version of TR-DOS patched to use the
+3's disk interface.
ROM 0 and ROM 1 can be used independently of the other ROMs on
modified 128 and +2 systems.
The machine will also include full international character
support (including from BASIC), 42 column text from BASIC in
256x192 mode, 85 column text from BASIC in 512x192 mode, support
for CP/M 3.0, and a user sizeable RAM disk (accessible from
BASIC using 128 or +3 commands).
- To what extent is it compatible with existing Spectrums and
clones?
Compatiblity is very important for the machine to be a success.
It will be PORT compatible with the original Spectrum but it
will also support the enhanced video modes of the TS2068 (which
are also used by some Pentagons), PLUSЗDOS, IDEDOS, TR-DOS (as
used on the Scorpion and Pentagon), the extended memory maps of
the Scorpion and Pentagon. The BASIC will support the commands
of the Spectrum, TK90X, Spectrum 128 and TS2068 in one mode.
Programs written for any of these machines can be loaded in and
RUN without modification in the standard mode. The BASIC will
also support the extensions of BASIC 64, which means that the
graphics commands will work in 512x192 mode.
- How much has been completed so far?
Most of the work so far has been spent on debugging the original
Spectrum BASIC and the 128 editor ROM. I've made some
interesting discoveries along the way, for instance, there's a
whole chunk of useless code in the 128 BASIC ROM (and hence in
the Pentagon, Scorpion, +2, +3 and +2A). In fact the original
BASIC ROM can be used with the +3/+2A without modification to
improve compatibility. On the 128 and +2 three bytes in ROM 0
have to be changed. It's amazing really. Anyway, back to the
question. The BASIC has been completely debugged. It is
certified 100% bug free. It has also been tested extensively
with a wide range of software for compatibility and no problems
have been found so far.
The ROM layout of the machine has been determined. The BIOS and
BASIC extensions live in ROM 0 (I'll also put the GUI toolbox in
there if there's enough room). BASIC lives in ROM 1 (even on the
+3 test version). PLUSЗDOS and IDEDOS (an extension to allow the
use of hard disks by Garry Lancaster) is in ROM 2. ROM 3 is
undecided. And I haven't decided how to implement TR-DOS support
yet. I could do it by emulation or by direct support (although I
will probably go for emulation for copyright reasons, this will
still allow TR-DOS software from the former USSR to run without
problems).
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For more information about the SE, visit
http://www.brandnewco.org/se/.
You can also contact Andrew at aowen@brandnewco.org to subscribe
to the 'SE-mail' newsletter.
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