Radio amateur 1/94
(c)Nemo.
SYSTEM BUS
IN SPECTRUM COMPATIBLE COMPUTERS
The problem indicated in the title is not
new Moreover, it is already quite
rela for a solution. A generally accepted
Spectrum bus standard. In this interest
re-signed as users (this will give them
wider selection of peripheral devices
roystvo), and producers (they will
ensured a significant increase in volume
sales activities).
Background and current status of samples
lems. Everyone remembers the epic associated with the
torture of computer expansion "Ra-
dio-8bRK". Due to the lack of design
system controller 58OBK28/38 (according to
society, also known as a bus controller) is missing -
There were also system signals for accessing
ports, which led to the need
fragmentation of the address space and uni-
cal circuit modifications of the computer itself
tera when docking each specific
devices.
The history of Sistema-360 is also interesting.
developments of IBM, which was the first to implement the
muzzle structure of the computer
lexa. Even having lost 13% of the sales market of the peri-
peripheral devices, IBM is more advanced than ever
it, strengthened its leading position in
industry [1]. In relation to domestic
In this situation, we note that only the power of IBM
allowed her to conduct her internal company
standard in the category of generally accepted methods
bom de facto.
System buses in Spectrum computersearly models and those currently produced
Bo are completely absent (“Leningrad-I”,
"Composite-48", 'KAY-128"), or brightly in-
individual (“Compact”, “The Hobbit”, “Le-
ningrad-II") and are incompatible with each other.
"Scorpi-" stands somewhat apart
on-ZS256", the developer of which considered it un-
still need to obey the corporate
standard, sacrificing for this purpose
public (~10 cm2) part of the area
chat fee. At least with Scorpi-
on'om join at least branded mouth-
swarms. The bulk of development companies
Chikov and now spreads the tire based on
convenience of tracing printed wires
kov, dooming himself to create a unique
periphery.
Peripheral developers
(HR-23, FDC-5, HART controllers disk-
yes, prototype - BETA DISK) output signals
on the tire so that they are light
to connect conductors with the uterine
(system) board, perhaps not at all
having a system connector. To avoid
confusion is used regularly
clock sequence of signals on the connector.
Generally speaking, machines of minimal con-
figurations are simply not adapted to stan-
forging external devices, first of all,
due to the design of the housing. However also
it is also undeniable that computers are maxi-
small configuration (with disk drive) must
We must have system slot(s). Ten-
trend toward gradual exclusion from the marketmachines of minimal design configuration
tions with the disk drive makes you seriously
think about the tire standard.
COMMERCIAL VISION OF THE PROBLEM.
As already indicated, production is inter-
compatible models of Spectrum machines and
peripheral devices benefit everyone and
will entail an increase in the total capacity
this sales market is for everyone who submits
standard, if there is one after all
will still appear. This is external, obvious
side of the problem.
A more detailed study of the issue
leads to the conclusion that the computer is
a dart tire will also have
higher consumer value
(PS). Let's consider this not entirely obvious
investigation in more detail. Moral term
computer aging - this value can be
considered proportional to PS - determines -
due to the obsolescence of the most critical
in this regard, nodes - peripheral devices -
swarms The more complete the configuration of single boards -
construction, the sooner it is morally
will become obsolete. A striking example of this is ATM. In idea-
Otherwise, the motherboard becomes obsolete
only by two parameters: clock hour -
tote (processor type) and information
system bus channel capacity, which, in general,
something, and led to the need for a change
IBM PC bus standard to its same standard
microchannel. This obsolescence is inevitable
as a congenital defect of any design with
von Neumann architecture.
Life cyclebus computer
can be significantly extended by successful
peripheral devices and their timely
replacement. Figuratively speaking, this can
turn a computer from a one-day butterfly
ki, at least in a butterfly-two-day-
ku.
Manufacturers of systemic (uterine)
boards that have transferred their market share to small
companies specializing in production
two peripheral devices (connected via
generally accepted standard) will receive equivalent
tape additional capital investment
and intellectual strength into your project with
very high efficiency.
A machine with a modular construction has
has higher maintainability. EU-
does a peripheral device fail?
yours, or even the motherboard, repair your
proceeds to a simple trial change of boards-mod-
lei. In the future, the failed module can be
replace through the manufacturer or
just throw it away. For reference: typical
The disk drive controller now costs a lot
significantly less than repairing the entire computer
ra entirely.
GENERAL ISSUES OF BUS IMPLEMENTATION.
The most authoritative prototype can be
consider a branded tire. And not at all because
her "overseas" origin. She got enough
definitely simple, practically tested, area-
provides the necessary, although not sufficient
functional completeness.
BUFFERING
LOAD CAPACITY
AND THE LOGIC OF WORK.
Buffering, generally speaking, is desirablespecifically. However, that share of the cost that
which will be included in the motherboard, de-
barks this is inappropriate. Should not be followed
it happens that the task of creating a tire is
for the computer, and not vice versa. Tire, in
first of all, there should be no burden
valid for a user to whom it is not
needed. The only acceptable option in
current situation - this is the output to the bus
as an interface LSI CPU (Z80) and
buffering (if necessary) with
side of the peripheral device.
The logic of the bus operation in this case is completely
is determined (with accuracy up to time)
variable diagrams and delay times) pro-
cessor element Z80 connecting the military
dino all modules. Problems associated with
standardization and documentation of para-
meters are resolved automatically by reference to
technical description of the Z80, which is generally
accessible and does not require any equipment
mentaries.
The experienced reader has probably already
has long had an objection related to the low-
what load capacity of the Z80. Days-
Therefore, output Z80 is enabled by load
press with no more than “one TTL input”. This
a serious disadvantage for the microcircuit, presumably
suitable for use as an inter-
face LSI. However, this limitation is easy
and, one might say, is removed elegantly
requirement to use as a load
Rusty on the tire ALS elements (series 1533).
Eight ALS inputs are equivalent to one
TTL input.Those. the entire bus line is provided with
It is possible to connect up to 8 units
ny loads, which is quite enough for
most practical applications. Red-
the type of ALS circuits to check is not so
rare, because Only the input parameters are important.
Here is a list of circuits identical in input
parameters of the ALS series: TTLSH-580, 589, 556,
158. It is also possible to use se-
ria 555, you just have to remember that one
A DTL input is equivalent to two ALS inputs.
A more complex question is about permissible amounts.
bone loads on the lines. Research
Research conducted by Nemo shows that,
for example, in Scorpion, which is simple
can’t be called a design, a reserve for
load capacities for the most loaded
address lines (A15) is 60 - 70%
(60 - 70 pF), for data - about 50% (100
pF). Particular attention should be paid to the computer
computers "Leningrad-I", "Composite-48" and
"KAY-128". Unbuffered keyboard
introduces about 40 pF capacitance on the address line
ty (flat cable about 25 cm +
40-key keyboard), which is practically
completely exhausts the loading method -
the presence of address lines and does further
expansion is very problematic. For
computer with an open, modular structure
keyboard buffering is strictly required
interesting.
Distribution of functions between maternal
which board and peripherals. The problem is lying
which is fundamental is, firstly, the definition
tion is minimalrequired configuration
Sinclair-compatible machine and, secondly,
would such a configuration be optimal with
a variety of points of view.
In Scorpion, for example, the controller
disk, 256K memory controller and sound
The processor is classified as a system device.
twam and are located on the motherboard.
Everything else that can be docked,
belongs to the periphery. This is one point
vision. The author attributes the controller to dis-
kov to obligatory, but still peripheral
radio devices. This is a different point of view
nia.
Generally speaking, the line between system
and peripheral devices is determined
built-in system mat. provision, in
first of all, and the accumulated amount of the ori-
application software based on it.
Focusing on the proprietary ROM Spect-
rum-128, can definitely be attributed to the control
disc roller to peripheral devices.
Creating a shadow monitor (in Scorpion)
allows you to look at the problem in a different way -
mu. Successful introduction and active use
calling a bus will inevitably “squeeze” functions
motherboard and make it count
disk controller peripheral device
yours.
In conclusion, it should be noted that
much is proposed here for the first time (at least
at least in relation to Spectrum's
family), is very controversial and has not been tested
It is practically in mass production.
However, the author, first of all, sees in his
readers not pirates,appropriating ready-
great ideas in the form of developments, and people,
engaged in cruising in the field of electrical
ronics and having a certain craving for non-
ordinary solutions and the search for new ideas.
LITERATURE
1. Meet the computer. Per. with
English edited by V.M.Kurochkina - M.Mir,
1989, p. 172 - 173.
(C) Nemo and SKiM have already been developed by cons-
production KAY-128-BUSY, in which ideas, from-
stated above are practically implemented.
Simultaneously with the sale
the first batches of boards will be published
in-house bus standard. Implementation
bus has several additional signals
cash that is not included in the branded prototype
ne (and Scorpion'e), significantly expanding
defining its capabilities (up to the PDP). When-
a whole range of new circuitry has been replaced
solutions that make it possible to implement these re-
presses (with the same board dimensions as in
KAY-128).
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