Bus architecture Spectrum
(Concept).
(C) Nemo 1994
________________________________
"Marasmus was intense ..."
Unpublished.
"Sometimes it's hard to resist
pressures exerted to activate the various possibilities,
that "it would be nice too
have available. "It is real
danger that the desire to please
everything will stop the problem of a holistic project. I always
trying to figure out what price
have to pay for the resulting
win. It is necessary to compare the benefits and additional
implementation costs and easily
the presence of something in the system,
which leads to its increase.
Developers [language] with the
often fail. "
N. Wirth
Company (c) Nemo deliberately publish this document (and
without him almost a year), so that the reader could
realistically assess the amount of work done and the
correctness of design, which is now so obvious.
Laboratory method
measurement of capacity bus lines.
Existing empirical methods of calculating the capacitive load
tire micro-computers resemble more
ritual rather than an engineering calculation. Data on
insertion capacity conclusions ICs are often absent, and those
that are available to reflect not real impedances, but rather
the reluctance of the manufacturers responsible for the quality
of their production and is clearly overstated. Real-world
systems (eg, Spectrum) suddenly find themselves with workable
downright "astronomical" loads on the tires. At constant
reduction of input currents and speed logic (155 /
555/1533/1531) is now transformed into a capacitive load at the
main constraint in the capacity system. Virtually impossible
calculate the proportion of capacity introduced by the PCB
tracks and non-standard technical solutions. For all these
reasons and attempted to pilot the measurement of capacities.
The method is based capacity utilization tires as
vremyazadayuschih. Identification of specific quantities
produced by the analysis with an oscilloscope imposed by a
foreign key transients in real
system.
When fed into RES CPU
log "O" bus addresses and data transferred to the Z-state. Go
to the measured line connects the key to element OK, the
control signal CLC (3,5 MHz) and a current source. Specifying a
certain amount current source and measuring the increment of U
on the waveform over a period of t, we can calculate the
capacitance:
idt
C =
dU
(In this formula can be replaced
differentials in increments).
Capacitance introduced by the installation,
(Probe oscilloscope, circuit switching, etc.) is installed
using high-precision calibration capacitor at the measured off
line.
In the measurement taken
the following assumptions:
- Frequency of measurements is sufficient
small for the manifestation of the properties
long lines of print tracks.
- Frequency of measurements is sufficient
large in order to source
current is not shunted active
conductivities on the measured line. (It is from these
assumptions has been selected frequency 3.5 MHz, instead of 1
MHz, at which normalized capacitance loads
tires Z80).
- It is believed that the current source
perfect. The method provides
accuracy of about + / - 20%,
enough for practical purposes. The traditional empirical method
gives an error of about +100%, -50%.
Buffering tires.
Bus buffering increases the physical load carrying capacity,
but reduces logic power bus. Nebuferirovannaya bus of the first
type is the following advantages:
- Clear documentation (for
Essentially, there are already standard)
the logic and timing (reference Z80).
- A possible set of signals, generally speaking, only one.
- Compatible with proprietary peripherals: Beta-Disk, Kempston
Joystick and Kempston mouse, LPRINT III and
so on.
- Have sufficient physical
load capacity when used as a unit
load element ALS.
Requirements on the architecture and
circuitry of the motherboard,
imposed by the bus.
1) In light of the conference on December 7-9 as the basic
architecture of the optimal architecture AMSTRAD. By and large,
in baseplate must be logged sites
Supported by proprietary system software, hardwired into the
ROM on the card. In particular, RS, and MIDI interfaces, at one
time is not supported by the programming companies in the West,
it is hardly necessary. 2) A controversial issue is
availability controller TR-DOS. The author considers the
presence of the controller TRDOS inertia in the system board
stereotypes of Spectrum -
machine as a game console with
fast loading of programs. It is worthwhile to note that the
system slot occupied by the controller TRDOS, can later be used
a device that combines functions of TR-DOS and the IDE -
controllers. 3) The board must necessarily have CENTRONICS,
since According to the company IskraSoft, 50%
PC users are going to use it as a word processor.
4) The basis of circuitry must
be put to simultaneous digital
automaton, clock signals are formed on the D-flip-flops
(flip-flop) clocked by one clock. It is necessary for a minimum
spread of sync relative to the signals CPU.
It shall be 100% compatible motherboard and slots
boards. This partly solves the problem of the possible immunity
for the bus on lines (especially mode TURBO).
5) The processor must be running in
linear at least up to the cycle time, ie,
any piece of software should have immutable at runtime,
regardless of the phase of the video processor and the location
codes in the address space. This necessary for the organization
of work in real-time network AON, ADC / DAC - Fourier
transformation, speech synthesis. 6) Ability to synchronize
Video processor with an external source (perhaps), and the
whole machine at sequence F =
14 MHz). Need to synchronize with the TV-over: (controllers
overlay TV images) PAL / SECAM encoders.
System bus and
system connector.
Had to meet the publication in which these concepts appear
as synonyms. However, to a "two big differences," as
they say in Odessa. Point out the differences:
- The system connector can be
only one and, accordingly,
serves one peripheral
device. Optimal same number
slots on the bus - four;
- The system connector involves
arbitrary external constructive volume of the plug
device and must be able to work on the ribbon cable.
Expansion slots have a stringent design constraints.
Itself a motherboard designed for housing, and place it
Installation is rigidly regulated.
Lamella system connector
displayed on the outer surface
Corps. If this is not done, then
we can assume that it is not at all. Board peripherals and the
main board located in the same plane. Boards expansion on the
bus are set perpendicular to the main (Mother) board and placed
inside the housing; - The optimal arrangement for
system connector - "board" for
Bus - the system unit. System connector for an open
architecture is divided into two aspects: system bus interface
and external peripherals. Interface IRPR-M (CENTRONICS) is
regulated as GOST 27492-88, and OST 107.460831.003-87.
Standard describes the interface for
IP connectivity, and TPO - for connecting peripherals.
Some questions in the bus.
1. Type of physical connection.
Optimal connector - double row connector for direct coupling
with the PCB. Strengths:
1) height connectors
5mm smaller than the assembly
Have mates.
2) the cost of connector is redistributed to the parent
fee, presumably having
greater life cycle than peripheral.
3) greater mechanical strength of the compound than with other
known types of connectors.
2. Two optimal layout
motherboard.
The first layout - rows of contacts or bus line arranged in
parallel lines connecting the Keys ROM and CPU. With this
arrangement, we can obtain any wiring bus. The space between
the slots not being used, which leads to an increase Square
board. The second arrangement - (As in Next) - ROM and CPU are
located between the slots, and the area fee is reduced. PCB Bus
loses its randomness. 3. Point of interception.
Intercept point - the point of entry / exit, providing the
ability to modify the bus signals generated by the motherboard.
Point of interception can be assigned to any static line, which
has the appropriate gating signal. Physically, the point of
interception is implemented inclusion in the gap signal ballast
resistor about 430 ohms. When using unit loads such as ALS
branching factor is not reduced. The introduction of the CPU
cycle I / O wait cycles allows for the inclusion of chain
catchpoints on slots system bus at a signal IORQ,
which gives the geographical priorities of slots for port
space. Work peripheral to the point intercept by using gates to
the OK or OE - output. TRS - output may
with the appropriate inclusion,
emulate and MA, and OK. Catchpoints enrich the logic bus
without its complications and the introduction of additional
signals.
Possible problems with the bus.
1) In the TURBO bottleneck
may become the point of interception of
time delay.
2) Capacitive load on the line
could become critical (again
same TURBO).
3) timing issues
PAL - encoder, which has a multiple
rate (to eliminate moiré and
beats color).
Three subsets of signals.
1. The first subset - it
signals of CPU, the common denominator
All Spectrum-machines. Availability
All of these signals is strictly necessary.
2. The second subset - signals the system connector of
corporate computer. Includes
p.1., the point of interception of ROMCS and
IORQ, as well as additional sources of +12 V,-5V.
3. The third subset - includes p.2. In addition
there are empty contacts and additional signals. From practice
found that the signal is used extensively F (14 MHz).
Empty contacts expected
use as needed. For example, a computer KAY-256 TURBO introduced
a line TURBO.
Interconnection layout and tires.
Implementation of the tire is only possible
when linking the "system unit"
as slots are given essentially
vertical dimension. Layout
type "search" can hardly be
considered successful, because there are a large number of open
volume conductors and structural volumes, and in general
construction of low-tech. Trying to install on the hard drive
such a system will further exacerbate situation.
Some experience of using
tire Spectrum'e.
1) The mounting slots
to the motherboard, or they can be lost in transit.
2) buffering bus can
lead to conflicts of system
devices and the motherboard.
3) Controllers must use, wherever possible, the first
subset of signals.
4) It is undesirable to work with logical events, shorter than
the machine cycle.
The composition of the motherboard.
Distribution functions
between the motherboard and
slots.
In the motherboard must
enter the components of the basic model,
are sufficiently worked out and
"Bent". This is probably the basic architecture "Amstrad", ie,
the first 10 points of compulsory
requirements. The presence of these components is strictly
necessary software.
External connectors, good
board has a tough case
regulated the installation site, are installed on the
motherboard. This is in contrast to models available, allows
operation without a body. Dramatically increases
maintainability and reliability of your computer as a whole.
Niche signals required for a particular
slots must be formed in
it, even with the duplication.
Not all signals in all cases
life, and a minimal set that allows the peripheral device can
synthesize any conceivable signal Simultaneous with the
motherboard.
The size of the vertical slots
the height of the body,
which, in turn, high
2 drives (the idea of "slots").
It is curious that drives using 3.5, you can set so high slot
that build on the placer will not be possible, ie possible
technological protection without detriment to the interests of
the user (as it did Apple). The size of the vertical slots
implicitly defines a capacitive load tires and should be
restricted.
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