ZX-NEXT
Computer from the 90s.
(C) Slot Co.,ltd Leonid Ermakov
Konstantin Sviridov
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Since the advent of microcomputers
tera ZX-SPECTRUM (1982) has already passed
fourteen years old. During this time in mi-
more than one generation of per-
personal computers such as IBM-PC, and
our old friend ZX practically
the same as before. Therefore,
phenomenon in this venerable family
new computer "ZX-NEXT" from the company
Slot (Moscow) cannot help but cause
curiosity and even surprise: and for-
what? Do we need it now, in our
time, another 8-bit baby?
Let's take our time and
Let's look at the newbie.
Despite the fact that the PCZX-NEXT prog-
Fully compatible with ZX-Spectrum tablet
thanks to the original technical re-
In our opinion, it can easily be classified as a PC
90s. To make sure of this
just analyze the market
household personal computers. C
on the one hand it is very powerful in its own way
computing abilities IBM clan
on the other hand, the dying person is already co-
for the second year the Spectrum-compatible fleet.
Dear reader will object: there is
They also sell "COMMODORE AMIGA" (500;600;
1200, etc.), “MAC” appeared here and there
and "SPARС", but they threaten... Let's leave them
at rest for now. Those who wish to discuss
We advise you to carefully read
interact with a very interesting audience
a talk on this topic in one of the issues
"ZX-PEVIE".
The only limitation for ZX is
Spectrum in this market is the lowest
some screen resolution and non-standard
new keyboard. Large communication-
functional capabilities of IBM computers
in our country it is not yet possible to implement
simple. Domestic telephony is not enough
adapted for use
for its intended purpose, not to mention
serious communication. And the prices for
high-quality modems, more or less
suitable for our lines, bite
(a fairly advanced modem like
ZуXEL costs about $700 USA). Is-
using cheap modems with low
mitransfer speeds are disappointing
vayet. Taking into account the length
programs for IBM and communication quality
it is often more rational to drive up from
with your own floppy disks or hard drive.
Using ZX-Spectrum for computers
communications, very tempting, in per-
new view, up to now
limited by several factors -
mi. Firstly, difficulties with connecting
rejection of standard modems due to
absence of RS232 port. Secondly, not
possibility (before the advent of iS-DOS)
easy to write and use
software support. Application
homemade modems with non-standard
protocols has serious limitations
values and can only be used
for connecting similar PCs. In general
there are no objective reasons preventing the use
use of Spectrum - compatible
computers for communication.
All of the above has no purpose
downplay IBM's capabilities. However,
if you are not engaged in professional
locally 'CAD PСAD' or 'AUTOСAD', and
also you don't need accounting for
3000 people or more, or at worst
end, don’t trade (of course not
legally) programs, then IBM in Wa-
Our house will be mostly expensive
a toy. And since similar “toys”
ki" take up quite a lot of space, then
better buy a game console
"SEGA - MEGADRIVE".Of course, according to
all characteristics, including low
cost, Spectrum-compatible PCs
will be able to remain the most for a long time
mass computers in our country
no. However, their position is now serious -
but they staggered. There are no reasons for this
how much Oddly enough, but...
great damage was caused by production
tels of numerous PC models. For
the prototype, as a rule, was not taken
the most successful version ("BALTIK" 1988;
"ANGSTREM" 1991 ; "QUANT BC" 1993;
"MOSCOW 1987" ; "SANTAKA" 1990;
"DELTA C" 1991; "MOSCOW 128" 1989;
"PENTAGON 48" ; "PENTAGON 128"). About
workmanship is not to speak of
has to. This happens again
due to the fact that most basic
models had selected elements and
required setup. A in conditions
mass production is unacceptable
Limo.
Trying to make a PC suitable for
mass production was undertaken
adopted by the developers of the PLM 1556XM1.
However, the ease of assembly, unfortunately,
is the only advantage
like a PC. Failed prototype
("ВALTIК"), a lot of conceptual
errors (compressed screen, reduced speed
interference with overclocking
frequency, etc.), all this is done by the PC
this type is inconvenient for users
caller. If we add to this
incomplete programcompatibility
(again, due to a number of circuit design
any miscalculations), then it becomes clear
that the branded PC ZX-Spectrum is pre-
ascends according to the totality of characteristics
tic of his followers.
Attempts to make a PC with the Z80 have been made
were carried out not only within the framework of ZX Spec-
trum. Computers "PROFI" and "ATM" -
confirmation of this. But orientation
to the outdated CP/M system and a number
circuitry incidents are extremely
had a negative impact on popularity
these models, not to mention the impossibility
the possibility of their mass production.
In the background of this picture is a new PC
The ZX-NEXT stands out a lot. And it's not
only that the “standard” scheme
there are no motor vehicles here. Striving for
had the least originality
by the authors during development. Basics
attention was paid to reliability,
repeatability (lack of adjustment
ki), software compatibility. All
These problems were solved thanks to
application as a video process
ra Z80. This made it possible to refuse
from using large quantities
VA counters and fine logic.
By far the most attractive
ZX-NEXT is a slot-type design
tion. This is an obvious solution, long ago
used on many PCs
("APPLE 2", IBM, etc.), allowed
turn your computer intodevice,
acquiring certain additional
special features at the request of the user -
caller System bus ZX-NEXT
has the ability to install 4/5
slot (or other) connectors. All
seats for connectors on "ma-
Terinsky" board is electrically identical
tic. It is possible to use a connector
mov type SNP64(96), both two- and
three-row.
Practically
virtually all processor signals (ad-
resources, data, management). Except
In addition, system control signals
memory, video signals and some
others . Power (GND, +5V, +12V)
also output to the system bus.
This design allows for
connect peripheral devices
swarms in a “cold” way (i.e. without
turning on the soldering iron).
Open architecture makes it possible
use of almost any
former peripheral devices, including
number and non-standard. But even in use
running form (without controllers), "ma-
Terinskaya "board-computer minimal-
but the configuration is quite suitable for
use. There is no order in ZX-NEXT
or scarce microcircuits required
connection to the elementary base of the minimum
us. The main problem of Spectrum
removable - reliability of RAM operation -
solved completely, and without damagefor compatibility. Let's try to solve
cover this question in more detail.
In almost all personal
computers use two options
anta interaction of the processor with RAM
transparent (RAM operates at speed
processor or faster) and non-
transparent (RAM is slower
processor). Both options are a compromise
dreams, that is, have their own merits
qualities and disadvantages. The main advantage
the advantage of the first option is the absence
reducing system performance. Not-
wealth is increased tr-
requirements for RAM characteristics (not
large variation in sampling time) and
circuit difficulties. Second
the method is less critical to parameters
RAM, since the processor when writing or
reading may have wait cycles
( WAIT ), but reduces performance,
which is especially noticeable on Spectrum-
compatible PCs.
A very significant point, decided
in ZX-NEXT, is a reduced
RAM regeneration time. The reason is many
many troubles associated with failures in RAM,
for Spectrum-compatible is
extremely long regeneration period
dynamic memory. It is determined
meter conversion factor
video processor and for standard
screen ( 256*192 + attributes ) is equal
2048 μs. For chips like KP565PU5
(4164) andKP565PU7 (41256) max.
short regeneration period no more
2 ms.
Using standard circuitry
getting a shorter period is very pro-
problematic. But with the use of Z80 in
as a video processor, this sample
The problem is easily overcome. Therefore in PC
ZX-NEXT average regeneration time
about 0.5 sec. Adding to this co-
advanced memory management scheme
we get a very interesting result:
in ZX-NEXT it is possible to use
RAM chips with a wide spread
sampling time in any combination.
For example: KP565PU5 B, V, D, D, E on one
no board.
Using the Z80 as a video pro-
the processor made it possible to solve a number of circuit
technical problems: not required
selection of a timing capacitor
to INT, FLASH generator settings.
Moreover, the flickering period is synchronized
van with frame scan. Therefore
there is no unpleasant information completely
interference, always stable and not
The FLASH period requires correction. Vi-
de-signals generated by PC ZX-NEXT
comply with accepted standards
(frame blanking, cut-ins, etc.).
The frame output is output to the video connector.
sync pulse, direct and inverted
bathroom synchro mixture. Number of lines in
frame corresponds to branded fashion
lam and standard(312 lines instead
320 for most other PCs). This
had a positive effect on accuracy
system clock based on period
ode to interruptions, which in ZX-NEXT
exactly corresponds to 20 ms (50 Hz
instead of 47.5 Hz for most others
Spectrum-compatible). Correct
time position and duration
INT signals had a positive effect
on video effects in many programs
mach (no sprite jitter,
correct position and shape of the curb
nal effects).
With these obvious advantages
managed not only not to increase
number of chips, but even reduce
their number. Compared to shi-
The popular "PENTAGON-128"
ZX-NEXT saves you at least
17 microcircuits, and there are additional
additional device modes (port
loadable RAM, full RS232,
improved TR-DOS controller, etc.)
Lack of selectable elements
makes the ZX-NEXT PC suitable for
production, facilitates sa-
independent assembly.
Among the pleasant little things we can note
presence on the board of a ready-made RGB-formi-
rovator, provided for the possibility
keyboard buffering, inter-
face KEMSTON-JOYSTICK.About the post-
last thing needs to be saidespecially .
The fact is that used in pain
Most game programs address 1Fh
used in many domestic
PC. This tradition goes back to
PC "BALTIK", where the manipulator was first used
was connected to KP580BB55. At the same time
address of port A in the chip, the same
gives with address 1Fh. However, first
source, that is, in the corporate
trinity "KEMSTON-INTERFACE" address
manipulator DFh. No anti-
speech with software
not here. The reason for this is the ad-
resizing I/O ports using
created in ZX-Spectrum. According to this me-
to select the peripheral device
trinity requires activation of the signal
CPU cash: IORQ, RD/WR and one of
bits of the lower half of the address bus
sa. For example A0="0" ( FEh ) use
used for keyboard addressing
(in particular). A discharge corresponding to
behind KEMPSTON is A5="0" ( DFh ).
When contacting the address 1Fh A5 also
is activated (compare DFh =
BIN 11011111 and 1Fh = BIN 00011111).
However, there are many programs available
where to contact KEMPSTON-JOYSTICK
at DFh ( "ATLANTIDA 1/2" ;
"DIAMOND" ; "NONAMED" ; "HOSTAGES" ;
"NAVY MOVES 1/2", etc.), while on
those PCs where the interface is connected via
address 1Fh, it is not selected. By
for this reason, choosing in programs
optionKEMPSTON on PCs such as:
"PENTAGON 48" , "PROFI" , "ANGSTREM"
(all PCs assembled on chips
1515XM1 or f6006), be prepared for
that he will be inactive.
PC ZX-NEXT, thanks to the correct
addressing, these shortcomings do not have
et. However, it has a full port
FFh (attribute port). Moreover, the real
This port is called the same as on the corporate
On my PC ZX-Spectrum. Thanks
this makes it possible to launch
many programs that do not work on
other models ("ARСANOID 1"; "TOP
GUN"; "SHORT 2"; "MANCHESTER UNITED"
etc.).
Availability of ports non-standard for
ZX-Spectrum, designed for management
controlling additional devices -
mi and modes, can impose non-
which restrictions on software
compatibility. This may also
live the cause of crashes and freezes
programs designed for use
use on a PC with an incorrect ad-
relocation of ports (for example, "Lenin-
deg-1"). To use similar
new software on ZX-
NEXT is blocked from
writing and reading all additional
ports. Thus, the hardware con-
the configuration can be changed in the pro-
process of work and is configured for con-
specific program.
Forfull software compatibility
ty with ZX-Spectrum, the contents of the ROM can be
zhet, with correction of differences, re-
go into RAM (similar to ROM SNA-
DOW IN IBM AT). It could be there
any DOS loaded (version TR-DOS and
etc.).
RS232 port implemented in ZX-NEXT,
fully software compatible with
similar device in branded
PC ("SINCLIAR 128"; "AMSTRAD 2+";
"AMSTRAD 3+"). In addition, he is
is standard from the point of view
electrical characteristics, although not
requires additional power supply -12V
(converter from +12 to -12 sov-
wound on the board). RS232 is implemented as
for input and output, while
proprietary software is used
support from 128K ROM. Therefore,
la possible work (without additional
difficulties) printer waste
lit BASIС 128. Printer routines
in ROM 48K also modified for use
use no longer requires a connection
Reading of additional devices such as
LX PRINT.
Despite the fact that ZX-NEXT is the most
more software compatible with firmware
desktop computers of the ZX family
Spectrum, it implements many
many functions that allow you to call
give it a computer from the 90s.
Providedexpansion of operational
memory up to 512 kilobytes,
moreover, management of additional
pages possibly in several ways
by ourselves. The first way is to increase
number of segments from address C000h. For
control them in port 7FFDh for-
categories D6 and D7 are valid. Pre-
motren their blocking for complete
software compatibility.
Full replacement possible
RAM for additional pages. Is-
using this mode you can run
TR-DOS from iS-DOS. If with 128K RAM
Possible use of bootable RAM
either with OS loaded or with DOS, then
with 256K and more, downloading is available in
DOS and OS RAM at the same time. Both that and
other options are very simple to implement
growth and allow placement in "ROM"
additional utilities. For example:
national character generators, prin-
Turn and keyboard routines
(for use of non-standard
keyboards). Moreover, the loading is similar
nal utilities can be produced in
the process of running programs. About everyone
options for using additional
RAM modes, complete information is given
dena in the technical description.
To increase performance in ZX-
NEXT TURBO mode is implemented, with
This doubles the clock speed of the Z80 -
sya. Switching to TURBO and back is possible
wife as hardware (button onbefore-
panel), and programmatically (OUT
to the port). Moreover, all transitions are possible
we are dynamic during execution
programs.
For normal operation, additional
devices when accessing ports
clock frequency decreases. This is pos-
agrees not to impose additional
requirements for the periphery (for example in
PC "PROFI" and "ATM-TURBO" in mode
Not all KP1818VG93 work TURBO).
About the features of the dis- controller
PC ZX-NEXT drive must be dis-
to say in particular. Thanks to the circuit technology
speed solutions
head coverage has been doubled.
This not only increases speed
work, but also greatly reduces noise.
The original two-phase PLL is
greatly improves the quality of reading and does not
contains burnable (and not very
reliable) K556PT4. For the first time among the con-
rollers TR-DOS applied two times
no pre-compensation when recording. This
the solution allows you to improve recording on
medium and poor quality media
va.
The controller is free from many non-
wealth, which have become almost
familiar to the user: when turned on
power supply and RESET output are not
TR-DOS no false appeal to dis-
to the driver. MAGIC works from any re-
press (even without initialization).Voz-
You can RESET DOS from BASIС 128.
In addition to the standard video mode ZX-
Spectrum 256*192 in PC ZX-NEXT pre-
advanced graphics mode is available
ki CGA 640*200. This mode is intended
important for full implementation
text editors. Screen address
sation is completely similar to CGA, which
made it possible to use ready-
high character generators. Mode 640*200
made it possible to implement communication
special programs designed for
working with BBC and other information systems
ny systems.
If you have 512K RAM to accommodate
There are 16 areas available on the screen, which
significantly increases opportunities
use. With connection to port
that RS232 NS modem (with software
support), PC ZX-NEXT can use
change like a standard element
information system type BBC.
A significant disadvantage of all Spec-
trum-compatible is non-stan-
dart keyboard, which is difficult
use for Russification
programs. Therefore, for ZXNEXT the development
nerd IBM keyboard controller,
which works in everyone, including
le and standard modes. At the same time
it is possible to load any matrix matrix
Vish for customization
program This feature is implemented
in SETUP, there are also many
other options that allow you to change
rebuild a computer for specific
tasks.
SETUP to save the configuration
uses non-volatile RAM
timer KP512VI1. The timer clock is used
used in iS-DOS to enter
date and time in file attributes.Tai-
measures can generate non-maskable
interrupts, which allows you to use
it in any ready-made software
provision.
The IDE hard drive controller allows
the ability to connect HARD DRIVE practically
virtually any volume. Program
initial startup is located in ROM
and in the non-volatile RAM of the timer
characteristics of a specific
drive. Although there are several IDE hard drives
more expensive than MFM, due to its characteristics
ticks (data transfer speed,
access time, dimensions, weight,
energy consumption, etc. ) they pre-
ascend them significantly, not to mention
already about the fact that it is significantly more
horny MFM controller practically
compensates for the difference in price. Zaru-
there are already several refugee producers
MFM hard drives have not been produced for years and
controllers, preferring more modern
belt IDE, SCSI, ESDI.
With the advent of controllers on sale
high speedlocal network for
ZX-NEXT (transmission speed more
10 Mbaud, PK50, DMA), it will become possible
simple combination of ZX-NEXT PCs
to classes. The cost of such equipment is
incommensurable (5-10 times)
lower than the similar IBM.
Designed specifically for ZX-NEXT
switching power supply with possible
external switching on and off
niya.This property will be required with the advent of
development in widespread use
currently underway communication
controller. This board turns a PC
into a powerful telephone server, completely
replacing the functions of AON, answering machine
and databases. With connected prin-
It is possible to use a PC in
fax quality, which has a very low
cost and variety of features.
All the above options for deleting
could be realized thanks to the slot
design that facilitates expansion
development of the system with a minimum of costs. This
also allows you to connect
any devices and controllers,
developed independently.
In conclusion, I would like to say that
that the ZX-NEXT is equipped with full documentation
Mention with examples of use
devices and controllers.
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