New - ZX-NEXT home computer from the 90s

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    ║ ZX-NEXT - home computer ║█
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    ║ 90s ║█
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   Since the advent of the microcomputer
ZX-Spectrum (1982) has already passed thirteen
twenty years.  During this time the world has changed
more than one generation of personal computers
ditch like IBM-PC, and our old friend ZX
almost the same as before. Poe-
therefore the appearance in this venerable family
new computer "ZX-NEXT" from Slot
(Moscow), cannot but arouse curiosity
and even surprise: why? Do we need
now, in our time, another 8th time
row baby? Let's take our time
and take a closer look at the newcomer.
   Despite the fact that the ZX-NEXT PC pro-
Fully compatible with ZX-Spectrum, thanks to
original technical solutions
It can easily be attributed to the PC of the 90s.
To verify this, it is enough to
analyze the market for household personal
computers.  On the one hand, very powerful
powerful in its computing abilities
the IBM clan, on the other hand, is already dying
which year the Spectrum park is compatible.
Dear reader will object: there is
also "COMMODORE AMIGA" (500; 600; 1200 and
etc.), "MAC" and "SPARC" appeared here and there,
but they threaten... Let's leave them alone for now.
   Let's be realistic, call IBM household
computer - not possible. In order to
To verify this, just a little arithmetic
metics.  So, what do you need in the evening?
sit down and play, say, DOOM?
To begin, find $800 USA to purchase
at least 386 DX 40 with 4 MB of RAM and
not a very "fast" hard drive. And not on-
get the 286 for half the price. "DOOM" on
It won’t “suit” her.  Yes, and give for it
$400, let's face it, is reckless. Sell
It will be very difficult for her further. And it's not
only in prices. Those advantages that
gives IBM AT 386,486... use
very difficult. It is enough to pay attention
mania about how these PCs are used in
offices of many companies. In most cases
ev is a Lexi-type word processor
con", much less often - primitive accounting
Terek packages and spreadsheets. All
these applications do not require much
speed and computing capabilities
news
   The only limitation for
ZX-Spectrum in this market is the lowest
some screen resolution and non-standard
keyboard Large communication opportunities
capabilities of IBM computers in our country
It's still difficult to implement. Domestic
telephony is poorly suited for use
use for its intended purpose, not for
inWe are already talking about serious communication. Yes and
prices for high-quality modems, more or less
suitable for our lines, bite (do-
a completely perfect modem like ZyXEL hundred-
it's about $700). The use of cheap mo-
demos with low transfer rates dis-
enchants.  Taking into account the length
programs for IBM and the quality of communication, often
I think it’s more rational to drive up with your dis-
ketami or winchester.
   For these reasons, and because of
lack of software support, IBM in ka-
as a telephone server there is practically no
applies.  Moreover, constantly
PC turned on, with a working hard drive and
monitor quickly develops its re-
resource No one would think of using
use IBM as alarm control
tion, because sometimes such a watchman stands until
the face of what he protects.
   Using ZX-Spectrum for communication
cation, very tempting, at first
view, until now limited
due to several factors.  Firstly,
difficulties connecting standard
modems due to the lack of an RS232 port.
Secondly, the impossibility (before the appearance
iS-DOS) easy to write and use
software support. Application of sa-
model modems with non-standard proto-
Colami has serious limitations and can-
Can only be used for one-to-one communication
typical PCs. In general, there are no objective reasons
rank interfering with the use of Spectrum -
compatible computers for communication.
   All of the above is not intended to be accepted
explore IBM's capabilities. However, if you don't
are engaged in professional CAD PCAD or
AUTOCAD, and you don't need accounting
for 3000 people or more, or, at worst
end, don’t trade (of course it’s illegal)
galal) programs, IBM in your home
children, mainly, with expensive toys. And so
how such “toys” take up quite a lot
there is a lot of space, then it’s better to buy a gaming
second console "SEGA - MEGADRIVE".
   Of course, by all characteristics,
including low cost, Spectrum - co-
portable PCs may remain for a long time
the most popular computers in our
country. However, their position is now serious
staggered. There are several reasons for this.
   Oddly enough, but the biggest
harm was caused by producers of numerous
PC models.  For a prototype, as a rule,
not the most successful version was taken (“BALTIK”
1988 - "ANGSTREM" 1991 - "QUANTUM BK" 1993;
"MOSCOW" 1987 - "SANTAKA" 1990 - "DELTA"
S" 1991; "MOSCOW 128" 1989 - "PENTAGON
48" - "PENTAGON 128"). About the quality of the product
there is no need to talk about cooking.  This
again comes from the fact that
most basic models had a selection
new elements and requiredsettings. And in
conditions of mass production this is not possible
acceptable.
   Trying to make a PC suitable for Mac
owl production was undertaken once
by PLM 155ХМ1 workers. However, simplicity
assembly, unfortunately, is the only
great advantage of such a PC. Unsuccessful
prototype ("BALTIK"), a lot of conceptual
errors (compressed screen, reduced speed
action at high clock speed
etc.), all this makes a PC of this type
inconvenient for the user. If there is an increase
add to this incomplete software compatibility
tiability (again, due to a number of circuit designs
ical miscalculations), it becomes clear
that the branded PC ZX-Spectrum is superior
according to the totality of the characteristics of their post-
researchers.
   Trying to make a modern PC with the Z80
were undertaken not only within the framework
ZX-Spectrum. Computers "PROFI" and "ATM" -
confirmation of this. But orientation towards us-
old CP/M system and a number of circuitry
ical incidents have an extremely negative impact
based on the popularity of these models, did not
already talking about the impossibility of their serial production
production.

   In the background of this picture is the new PC ZX-NEXT
stands out a lot.  And it's not just about
that the "standard" circuit design is here
no.  Less desire for originality
the authors owned everything during development.
The main attention was paid to the reliability
ty, repeatability (lack of adjustment),
software compatibility. All these tasks
was solved thanks to the use in ca-
as a video processor - Z80. This allowed
Lilo stop using big
number of counters and fine logic.
   For a more detailed description of the PC
ZX-NEXT, we will try not to load the reading
lei with a description of the circuitry, focusing on the main
special attention to the benefits that
has PC ZX-NEXT ahead of other models.
   By far the most attractive
ZX-NEXT is a slot design. This
obvious solution, long used
on multiple PCs ("APPLE 2", IBM PC/XT/AT
etc.), made it possible to turn a computer into
device that acquires certain additional
additional features upon request
user. The ZX-NEXT system bus has
It is possible to install 4-5 slots (or
other) connectors. All seats under
connectors on the "motherboard" electrical board
identical.  Can be used
connectors type SNP64 (96), both double and
and three-row.
   Almost connected to the system bus
all processor signals (addresses, data,
management). In addition, system signals
memory management controls, video signals and non-
which are different. Power (GND, +5V, +12V),
also output to the system bus. Takaya
the design allows for connection
keeping peripheral devices cold
method (i.e. without turning on the soldering iron).
   Open architecture makes it possible
use of almost any peripheral
linear devices, including non-stationary
gifted.  But even in its original form (without
all controllers), "motherboard" board -
a minimally configured computer
suitable for use. Not in ZX-NEXT
custom or scarce microcircuits, required
The changes to the element base are minimal. Os-
new problem for Spectrum compatibles -
reliability of RAM operation - completely resolved,
and without compromising compatibility. By-
We are trying to reveal this issue in more detail.
   In almost all personal
computers use two options
interaction between the processor and RAM: transparent
ny (RAM runs at processor speed
or faster) and opaque (RAM running
slower than the processor).   Both options
compromise, that is, they have their merits
advantages and disadvantages. 
   The main advantage of the first option
- no reduction in system performance
topics.   The disadvantage is increased
requirements for RAM characteristics (non-
large variation in sampling time) and circuit-
technical difficulties.
   The second method is less critical to para-
meters of RAM, since the processor when writing
or reading may have wait ticks
(WAIT), but reduces performance, which
especially noticeable on Spectrum-compatible
computers.  Options for implementing pro-
cancerous and opaque modes of non-
how much  Examples of different video modes
are given in the table:

(for easier viewing of the table, click
 key "1")
╔═══════════════╤═════════╤═══ ═════════════════════════════╗
║Computer type │RAM mode│ Additional ║
║ │ │ features ║
╠═══════════════╪═════════╪═══ ═════════════════════════════╣
║ PENTAGON 48 │transparent│ Position of processor cycles and ║
║ PENTAGON 128 │ │video processor unorganized.║
║ Moscow 128 │ │Unused RAM cycles are under-║
║ │ │the video processor is shaking.            ║
║ Krasnogorsk │transparent│ Position of processor cycles and ║
║ZX-Spectrum 2+A│ │video processor is arranged in ║
║ AMSTRAD 3+ │ │res one.                       ║
╟───────────────┤ │ ║
║ ZX-NEXT │ │ The processor skips cycles vi-║
║ PROFI │ │deoprocessor in TURBO mode ║
║ ATM-TURBO │ │ ║
║ ATM-TURBO-2 ││ ║
╟───────────────┼─────────┼─── ─────────────────────────────╢
║ ZX-Spectrum │opaque-│ The position of the cycles is ordered ║
║ZX-Spectrum 128│chny │when accessing screen RAM, ║
║ ZX-Spectrum 2+│ │the processor slows down and reaches the windows- ║
║ Moscow 48 │ │video output (in line or ║
║ │ │screen) ║
╟───────────────┼─────────┼─── ─────────────────────────────╢
║ BALTIK │opaque-│ The position of the cycles is ordered, ║
║ ANGSTREM │the processor slows down when the ║
║ Leningrad 1 │ │deniation of video processor cycles and ║
║ Leningrad 2 │ │and M1 processor cycle ║
║ ZX-SCORPIO │ │ ║
╚═══════════════╧═════════╧═══ ═════════════════════════════╝

   A very significant point resolved
in ZX-NEXT, is the reduced re-
RAM generation.  The cause of many troubles is
with faults in RAM for Spectrum-co-
compatible, is an extremely large pe-
dynamic memory regeneration period. He
determined by the conversion factor
video processor counters and for stan-
standard screen (256*192 + attributes) ra-
ven 2048 µs. For microcircuits type KR65RU5
(4164) and KR565RU7 (41256) maximum
The regeneration period is no more than 2 ms.
   Using standard circuitry
obtaining a shorter period is very problematic
but... But using the Z80 as a video
processor this problem can easily be overcome
ma.  Therefore, in the ZX-NEXT PC, the average time
regeneration is about 0.5 ms.  Adding to
this is a perfect memory management circuit -
Well, we get a very interesting result:
in ZX-NEXT it is possible to use micro-
chem RAM with a wide range of selection times -
ki, in any combination. For example, KR55RU5
B, C, D, E, E on one board.
   Using the Z80 as a video processor
Sora made it possible to solve a number of circuit design
no problems: no selection of timing required
giving capacitor to INT, setting
FLASH generator, and the flickering period
synchronized with frame scanning.
Therefore, there is no unpleasant
interference, is always stable and does not
There will be a correction period FLASH. Video signal
ly formed by ZX-NEXT correspond
accepted standards (personnel cancellation,
insets, etc.).
   The frame output is output to the video connector.
sync pulse, direct and inverse
synchro mixture.  The number of lines in a frame corresponds to
complies with branded models and standard
(312 lines instead of 320 for most others)
gih PC).  This had a positive impact on
taccuracy of the system clock based on
interrupt period, which in ZX-NEXT
exactly corresponds to 20 ms (50 Hz instead
47.5 Hz for most other Spectrum -
compatible).   Correct position according to
time and duration of the INT signal
had a significant impact on video effects in
many programs (no jitter
sprite, correct position and shape
border effects).
   With these obvious advantages, successful
it was decided not only not to increase the number of micro-
roschems, but even reduce their number. By
compared to widespread
"PENTAGON 128", ZX-NEXT saves you mi-
at least 17 microcircuits, and there are additional
modes and devices (port
configurable RAM, full RS232, improved
upgraded TR-DOS controller, etc.). From-
the presence of selectable elements makes PC
ZX-NEXT suitable for mass production
water supply, facilitates self-collection
ku.
   Among the pleasant little things we can note:
presence on the board of a ready-made RGB-shaping
body, provided for the possibility of buffering
Keyboard settings, KEMPSTON interface -
JOYSTICK.
   Regarding the latter, it is necessary to say
get special. The point is that the used
in most gaming programs the address is 1FH
used in many domestic PCs.
This tradition goes back to PC "BALTIK"
(1987), where for the first time the manipulator was
connected to KR580VV55.  In this case the address
port A in the chip, matches the address
1FH.  However, in the original source, that is, in
branded device "KEMPSTON - INTERFA-
CE" address of the DFH manipulator. No pro-
software inconsistencies
not here. The reason for this is the address method -
tions of input-output ports used in
ZX-Spectrum.  By this method to select
peripheral device must be activated
visualization of CPU signals: IORQ, RD/WR and one-
th of the bits of the lower half of the ad bus
res.  For example, A0="0" (FEH address) is used
used for keyboard addressing (in
in particular).    The category responsible for
KEMPSTON is A5="0" (address DFH). When
contacting the address 1FH, A5 is also active
zited (compare DFH = BIN 11011111 and
1FH = BIN 00011111).
   However, there are many programs where
KEMPSTON - JOYSTICK can be contacted at
su DFH ("ATLANTIDA 1; 2"; "DIAMOND";
"NONAMED";  "HOSTAGES"; "NAVY MOVES 1; 2"
etc.), while on those PCs where the interface
connected to address 1FH, it does not select -
Xia. For this reason, choosing in programs
KEMPSTON option on PCs such as: "PENTAGON
48", "PROFI", "ANGSTREM" (on all PCs own
early on 1515XM1 or f6006 chips),
be prepared for the fact that he will be without
act.
   PC ZX-NEXT, thanks to the correct address-
sation, does not have these shortcomings. However,
has a full FFH port (attribute port)
Comrade). And the realitiesThis port is called the same
like on a branded PC ZX-Spectrum. Blagoda-
Because of this, it becomes possible to launch
many programs that do not work on others
models ("ARKANOID 1"; "TOP GUN"; "SHORT
2"; "MANCHESTER UNITED", etc.).
   Availability of ports non-standard for
ZX-Spectrum, designed for control
additional devices and modes
Mami, may impose some restrictions
software compatibility considerations. This
can also cause failures and
hangs of programs intended for use
use on a PC from an incorrect address -
tion of ports (for example, Leningrad-1).
To use such software
software, the ZX-NEXT has
blocking from writing and reading all additional
thread ports. Thus, the device is
This configuration can be changed in
process of work and customized to specific
new program.
   For full software compatibility with
ZX-Spectrum, the contents of the ROM can, with cor-
rection of differences, rewrite in RAM (ana-
logically ROM SHADOW in IBM AT). There we can-
Can be loaded with any DOS (version
TR-DOS, etc.).
   RS232 port implemented in ZX-NEXT,
fully software compatible with analogue
a convenient device in branded PCs
("SINCLAIR 128"; "AMSTRAD 2+"; "AMSTRAD
3+"). In addition, it is standard
from the point of view of electrical characteristics
tick, although it does not require additional food
Tania -12V (converter from +12V to
-12V is collected on the board). RS232 implemented
both for input and output, while using
uses proprietary software
support from ROM 128K. Therefore, it became possible
no work (without additional complications)
tey) printer utilities BASIC 128.
The printer routines in the 48K ROM are also updated
are working and can no longer be used
additional connection required
LX PRINT type devices.
   Even though the ZX-NEXT is the most
software compatible with branded computer
ters of the ZX-Spectrum family, it features
Many functions have been simplified to allow
call it a 90s computer. Pre-
RAM expansion up to 512K is envisaged, and
managing additional pages
possible in several ways.  First
method - increasing the number of segments with ad-
res C000H.  To manage them in the port
7FFDH bits D6 and D7 are involved. Pre-
provision is made for their blocking for complete pro-
frame compatibility.
   It is possible to completely replace the RAM
to additional pages.  Using
this mode can run programs
TR-DOS from iS-DOS. If with 128K RAM it is possible
You can use bootable RAM either with
loaded OS either with DOS, then with 256K and
loading into DOS and OS RAM is more accessible
at the same time.  ANDboth options
very easy to use and allow you to change
place additional utilities in the "ROM".
For example, national character generators,
printer and keyboard routines
(for using non-standard keyboards)
tour). Moreover, downloading such utilities can be
can be carried out during the operation of the program
ram.  About all application options before-
additional RAM modes full information
tion is given in the technical description.
   To increase performance in
ZX-NEXT implements TURBO mode, while
The clock speed of the Z80 doubles. Transition
to TURBO and back, possible in hardware
(button on the front panel), and prog-
frame (OUT to port). Moreover, all transitions
possible dynamically, during execution
programs.  For normal operation up to
additional devices, when accessing
ports, the clock frequency decreases. This
allows you not to impose additional
requirements for peripherals (for example in a PC
"PROFI" and "ATM-TURBO" in TURBO mode work
Not all BIS KR1818VG93 work).
   About the features of the drive controller
The ZX-NEXT PC needs special mention.
Thanks to circuit solutions, speed
Increased drive head positioning
doubled. This not only increases
speed of operation, but also greatly reduces
noise.  Original two-phase PLL su-
significantly improves the quality of reading and does not
contains burnables (and is not very reliable)
nykh) K556RT4. For the first time among controllers
TR-DOS, two pre-compensation times applied
sations when recording. This solution allows
improve recording on medium and
poor quality.
   The controller is free from many shortcomings
tattoos that have become almost familiar
users: when turning on the power and
exit via RESET not in TR-DOS, there is no "false-
th" access to the disk drive. MAGIC works
from any mode (even without initialization)
tions). RESET DOS from BASIC 128 is possible.
   In addition to the standard video mode
ZX-Spectrum 256*192, PC ZX-NEXT is pre-installed
Motren advanced graphics mode CGA
640*200. This mode is intended for half-
valuable implementation of text editors.
Screen addressing is completely similar
CGA, which made it possible to use
ready-made character generators.  Mode 640*200
allowed to implement communication
programs designed to work with
BBS and other information systems.
   If you have 512K RAM to accommodate
16 areas are available on the screen, which is
significantly increases the possibilities of
use. With connection to RS232 port
HS modem (with software support in
iS-DOS), PC ZX-NEXT can be used as
standard elementinformation system
We're like a BBS.
   A significant disadvantage of all Spectrum
- compatible is a non-standard class-
viatura, which is difficult to use for
Russified programs.  Therefore for
ZX-NEXT developed IBM keyboard controller
tours, which are in everyone, including
standard modes.  In this case it is possible
loading any key matrix for
settings for a specific program. This
the function is implemented in SETUP, where
There are many other options that
allow you to rebuild your computer for
specific tasks.
   SETUP to save the configuration using
uses non-volatile timer RAM
KR512VI1.  The timer clock is used in
iS-DOS for entering the date and time into the at-
file attributes.  The timer can generate
non-maskable interrupts, which allows
apply it in any ready-made software
provision.
   The IDE hard drive controller makes it possible to
the ability to connect HARD DRIVE is practically
any volume.  Initial program
start-up is located in the ROM, and in the energy storage
The dependent RAM of the timer stores the characteristics
tics of a specific drive. Although IDE Windows
ters are somewhat more expensive than MFM, due to their characteristics
characteristics (data transfer speed,
access time, dimensions, weight, energy
government consumption, etc.) they exceed them
significantly, not to mention the fact that
significantly more expensive MFM controller
practically compensates for the difference in price.
Foreign manufacturers have already
MFM hard drives have not been produced for years and
controllers, preferring more modern
IDE, SCSI, ESDI.
   With the advent of controllers on sale
high speed local network for
ZX-NEXT (baud rate more than 10 Mbaud,
PK50, DMA), simple processing will be possible
combining ZX-NEXT PCs into classes. Cost
similar equipment is disproportionate (in 5
- 10 times) lower than that of IBM.
   Specially developed for ZX-NEXT by him-
pulse power supply with the ability
external switching on and off.  This
property will be required with the advent of widespread
who is currently developing
communication controller. This board
turns your PC into a powerful telephone server,
combining the functions of Caller ID, answering machine and
databases.  With a printer connected,
it is possible to use a PC as a factor
ca, which has a very low cost and
various functions.

   All the above possibilities were possible
realized thanks to the slot design
tion that facilitates system expansion with
minimum costs. This also makes it possible
ability to connect any devices and
controllers developed bybridge-
specifically.

   In conclusion, I would like to say that
that the ZX-NEXT is supplied with complete documentation,
with examples of using devices and
controllers.  For purchasing questions
computers, empty and assembled circuit boards
Contact the company "SLOT":

        117330 Moscow PO Box 707

          tel. (095) 143-11-91

*****************************************
L. Ermakov, K. Sviridov Slot Co., Ltd, 1994
             kiSSSoft 1995
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