WHAT ARE CARTRIDGES?
The Atari ST computer is equipped with one of the
best ranges of I/O connectors of any personal computer, including
parallel, serial, MIDI and DMA ports. Independent companies have
brought out software and hardware to enable you to make the best of
each of these connectors with the exception of the cartridge port.
Eight-bit Atari owners will already be familiar
with cartridges, a method of using programs on ROM (Read Only
Memory) rather than loading them into RAM from disk or cassette. The
128K cartridge port on the ST is, however, both bigger and more
flexible than the 8-bit machines 16k cartridge and can contain more
than one program. On the 8-bit Atari, each cartridge would dominate
the computer so that, when you had a Star-Raiders cartridge in, for
instance, you could not also load a word processor from disk. On the
ST, whilst the cartridge can take complete control in a similar
manner, it may also be used in a manner similar to a disk drive
(i.e. the program is only run when you choose to do so), or as a
method for loading accessories.
So that's what a cartridge is used for, but what
exactly is a cartridge? Well, it is quite simply a printed circuit
board (PCB) with two or four ROM or EPROM chips, suitably
programmed, with a case around it. An EPROM is an Erasable
Programmable Read Only Memory, and it provides a re-usable ROM. ROMs
are cheaper than EPROMs, but when you are developing a program you
do not want to keep throwing away a chip costing five pounds every
time you want to make a small change.
On one side of the cartridge is a connector which
makes contact with a matching connector in the slot on the left side
of your ST, and which connects the ROMs directly into the memory
space of the 68000 processor. When the ST is booted (turned on) the
operating system (O.S.) looks at this area of memory and tries to
find a cartridge, taking appropriate action it one is found.
Plugging in a cartridge and booting up will cause a new icon to
appear on the desktop, very similar in operation to the disk icons,
but with the identifier 'C'. Opening this shows you what programs
you have on the cartridge. To run a program, just open it in the
usual way. Note though that, unlike opening a file from disk,
opening the cartridge program does not load it into RAM, it is run
straight from the ROM and therefore it is exceedingly fast to 'load'
and most of your RAM is available for data. Computer Concepts Fast
ST BASIC is run by this method (I understand Computer Concepts used
the Nexus EPROM development system). The program can be any of the
usual types, i.e.. APP, TOS or TTP. If the program is an accessory,
it can be run by selecting its name in the DESK menu (BackPack, a
multi-purpose utility, also from Computer Concepts, uses this
method).
Cartridges are obviously very fast to load and
easy to use, so why are there so few about? The reason is partly
that it is difficult to write a program to go into a cartridge, and
partly that there has been no ST cartridge development system. Nexus
has now removed the latter problem, and the rest of this article
will review their development system.
NEXUS EPROM DEVELOPMENT SYSTEM
The Nexus EPROM Development System (hereafter
called NEDS) is designed to provide a method of testing, simulating
and programming EPROMs. Very cheap EPROM programmers that plug into
the side of computers are available, so the question that must be
asked is what can this system do that a cheaper system cannot? The
answer lies in the test and simulate part of the description.
TESTING AND EMULATING
The NEDS has 64Kbytes of RAM on its 7 inch by 10
inch uncased PCB, as well as two Zero Insertion Force EPROM sockets,
two 28 way simulation header sockets and the required logic chips.
The RAM is used to hold the program and/or data that you want to be
programmed onto the EPROMs (programming of 128K cartridges has to be
done in two stages). The clever part of the NEDS is that this RAM
can be made to simulate a ROM, either on the host system (the one
into which the NED S is plugged) or, via the 28 way headers, in an
external system. By either of these methods, it is possible to test
your program in (simulated) EPROM without going to the trouble and
expense of 'blowing' an EPROM, and then having to erase it if it did
not work. The contents of the NEDS RAM will survive a reset and, for
longer term development, can survive without power for up to two
weeks.
IN USE
To use the NEDS, you must first plug it into the
cartridge port, and then turn the computer on. You then load
EPROG.PRG from disk, and you are presented with a GEM dialog which
contains a list of all the different EPROM types and programming
modes available. NEDS will program three different types of EPROM
(2764, 27128 & 27256) in one of two ways, and they can be in
8-bit (for processors like the 6502) or 16 bit wide modes (for the
ST). After making this initial selection, a window is opened in
which a memory dump of either the EPROMs or the simulation RAM can
be obtained, and five icons appear on the left hand side. These
icons represent the EPROMs in the ZIF sockets; the simulation RAM
(depicted as an icon of the four-legged woolly variety of RAM); a
floppy disk; a screen; and an AUX (serial) port. These are used by
dragging one on top of another. For instance, to program your EPROMs
you would drag the disk over the RAM, select a file (which can be of
INTEL hex, MOTOROLA hex, Hex space or binary type, a demo binary
file is included on the disk) and then when the file is loaded, drag
the RAM over the EPROM to make the permanent copy. The EPROMs can
then be put in a cartridge board (which Nexus can supply). To see
the contents of the EPROM, you drag the EPROM icon over the screen
icon. The memory can be scrolled for viewing using the windows
scroller bar.
As well as the icons, NEDS has a full complement
of drop down menus. These allow you to: change the EPROM type; check
the EPROM is blank, or programmed correctly; locate a byte (or word)
in RAM or EPROM; perform a checksum of EPROM or RAM; fill or clear
RAM; move RAM block; edit RAM; display the memory either as bytes,
word or longwords; and set the simulation mode. Most of the
functions allow you to specify a range to operate within, and all
use a 'thermometer' to indicate progress.
In general you are able to do everything that you
are likely to want to do to program EPROMs and simulate them. The
RAM editor is very simple, and is only adequate for changing a few
bytes, not extensive changes, there is no disassembler or assembler
provided.
The major software deficiency at the moment is an
automatic mechanism for converting your compiled language code into
a form suitable for use in an EPROM. A special header is needed in
the EPROM for the O.S. to recognise it and be able to use it, as
well as initialisation code. Unless you are familiar with 68000
machine code, and with the initialisation method of your compiler,
you may have trouble writing code for this part of the process.
Nexus ask that any such software you write for the public domain be
sent to them for inclusion in their package. I hope that people do
this, in order to encourage less experienced users to use the
system. Nexus are also considering releasing (at extra cost)
compiled libraries of their simulation RAM read/write routines used
in the programmer, to be used by the very advanced programmer who
wishes to write his own utilities to work with the Nexus board.
THE MANUAL
The manual is supplied on disk as a file. The
single sheet of instructions that comes in the package instructs you
to select one of three programs depending on whether you want to
have a copy on your parallel or serial printer, or on the screen.
The manual assumes that you are familiar with EPROMs and EPROM
programming. It gives no information about what is required from a
cartridge to make the O.S recognise it, only a book reference is
given (I also recommend Atari's 'Hitchhikers guide to the BIOS'). I
hope that Nexus provide a section with full detail about this in
future, as there is only a limited amount of information available
on this subject, and it would encourage sales if you knew that you
would get more detail with the system. The manual does however cover
operation of the NEDS hardware and software quite adequately.
CONCLUSION
The Nexus EPROM Development System is a very
capable EPROM programmer and simulator. I would certainly recommend
it as such. The word development in its title is a bit misleading as
it is not complete, lacking the software to make a cartridge header
version from a standard linked version. A few utilities, or a new
startup source for a compiler to provide this function are needed.
The system is not for the beginner, but is very reasonably priced
when considered for use by a software developer.
The Nexus EPROM Development System costs £201.25,
socketed ST cartridge boards cost £14.75 and 28 way DIL plug EPROM
simulation leads cost £11.50 (all prices include P&P and VAT)
top
