ZX=DIGITIZER
(C) V.M.Getmanets "RadioAmator 10/95"
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EDITORIAL:due to the peculiarities of output to
article content screen and inability
fully support the display standard
names of computer signals and
schematic subtleties used in
all printed circuits, it was decided instead of the top
her features use underscore-
tion. This disclaimer is valid ONLY
for articles from the "iron" section.
WHAT IS THIS?
==============
"Digitizer"is a device
converting video signal into digital format
mu for further processing on a computer
yutere. The proposed device allows
observe on the computer screen ZX-Spect-
rum black and white television image
inreal time (50 frames per second)
in digitized form - in various gradations
brightness corresponds to different densities
dots (pixels) on the screen. Current frame
is located in the video RAM of the computer, which is
knows how to print it on a printer,
and record it on magnetic media for
further processing.
The device interfaces with the ZX-Spectrum
cut system connector and does not require any
modifications to the computer.
OPERATING PRINCIPLE
==============
The video signal to the device input is supplied by -
from the input of the video detector of the radio channel
Levizor, which runs idle when
using a TV as a monitor
tora. You can also send a signal from the output
yes TV camera or VCR. Pre-
There are two ways to access the ZX-Di-
gitizer: hardware (by closing the re-
switch) and software - at the time of recording
send any number to port #F7 current frame
stored in video RAM.
The image consists of 256x192 pixels,
attributes are not used. Part of the image
area corresponding to the outer frame of the screen
to (BORDER), is not written to RAM. Ga-
guaranteed number of gradationsbrightness is not me-
she's 6.
An important advantage of this device is
va are the simplicity of design and support
connection to a computer, ability to work
in real time, two ways to control
tions - hardware and software, possible
the ability to transmit gradations of image brightness
nia, absence of scarce parts. The most
the main disadvantage is the orientation
to computers with a common memory field: "Le-
ningrad", "Pentagon", "Baltic", "Baltic",
"Pro" and others. For computer owners
ters with separate memory fields like
"Krasnodar", "Lvov", "Orizon-micro" and them
similar in the "ZX-Digitizer" circuit there is
a certain redundancy (formation
signals WR, RD, A15), allowing the production
carry out individual adaptation of the device
for any model. Moreover, the scheme
it is not difficult to adapt these to the regimes of increased
high resolution available on the computer
rah "Profi" and "ATM-turbo", but this is
is beyond the scope of this article.
Important and unusual, according to the author,
in this development is the use
for digitizing images analog-to-digital
second conversion (ADC) amplitude -
duty cycle, widely used in circuits
pulse voltage sources. Additional
Using an ADC with an interlaced bass reflex
allowed to significantly improve the quality
digitized image. New (with
all apparentobviousness) also appeared
the idea of hardware implementation of direct access
pas to the computer memory, which allowed installation
ability to work in real time
me.
SCHEME DESCRIPTION
==============
All signals, except DOS and 7 MHz, are supplied -
to connector X1 from the pins of the Z80 processor.
A bar above the signal name means that
its active level is low. Signal hour-
totoy 7 MHz is taken from the corresponding
counter or trigger TM2, which is
located on the computer board. About the DOS signal
more details will be discussed below.
Write to port 247 (#F7) and press the button
ki K1 leads to reset of trigger DDZ.2.
In this case, the BUSRQ signal is activated, which
which disconnects the Z80 processor from the buses,
converting its outputs to the Z-state. Released
div bus, the processor sets the signal BU-
SAK to input D of chip DDCh.1, activated
activating the AEN signal, which allows digital capture
address bus timer. Simultaneously with
with this, the horizontal sync pulses begin to
step through element DDb.4 onto the trigger
DDЗ.1 and install it in a single connection
standing, thereby allowing the operation of the burner
zontalcounters DD1.2 and DD2.1, from -
reading the number of clock pulses in
one line. The signal is also removed
reset from "vertical" meters DD1.1 and
DD2.2, which count the number of lines.
After counting 64 lines (BORDER on top
screen) V6 signal through elements DD8.2 and
DD8.4 resets vertical counters and
trigger DDCh.2. Now the countdown begins
192 lines of Sinclair screen accompanied by
driving low VEN signal level.
Simultaneously horizontal counters
count 96 clock (7 MHz) pulses
from the front of each horizontal sync pulse
sa as the left BORDER. During
the next 256 clock pulses, corresponding
corresponding screen area, on the 6th vy-
water of the DDS.1 chip is maintained low
cue level. Low level on this output
where, together with the VEN signal, it allows the output
data to the DD1.4 bus and the formation of a signal
cash MREQ and WR DD11, which leads to
writing the generated data to that cell
screen area of computer RAM, address
which is currently displayed on DD14
and DD15.
Please note that before this activity
the RD signal was sighted and the address A15 indicated -
goes to the top half of the RAM. This is necessary
dimo for carrying out the regeneration process
RAM in computers with a separate field pa-
wrinkle. WR signals are generated for them,
RD and A15. For computers with sharedfield
there is enough memory so that the first two sig-
Nala always had a high level, and tr-
tiy is always low. This can be achieved -
Xia, if WR and RD are connected to the power bus
+5V with 3/10 kOhm resistors, and to the output
4 DD16 microcircuits supply zero level.
After finishing writing to RAM the last
line signal from element DD8.1 through ele-
ment DD7.3 sets triggers DDЗ.2 and
DDCh.1 to its original state, blocking the
bot of the digital part of the ZX-Digitizer circuit.
The BUSRQ signal is removed and the bus control
mi is transferred to the Z80 processor.
The analog part of the device consists of
pre-amplifier VT1, emitter-
repeater VT2, amplitude detector
torus (sync selector) VT3 and
output video amplifier VT4. From
denominations of differentiating elements
filter C5, R12, R13 and R14 depends on the type
pictures on the screen. When R12=0 we have maximum
the maximum number of brightness gradations (differential
there is no Renting), and C5, R13 and R14 then
not needed. In the absence of R12 it turns out
outline picture, similar to a child's
drawing.
Pulses are formed on element DD10.4
sys with a frequency of 3.5 MHz, the phase of which varies
varies 180 degrees from line to line.
The integrating chain R17, C9 gives them
pulses have a sawtooth shape, and the comparator
DA1 compares the sawtooth levelim-
pulse at input 3 with brightness level
signal at input 4. The higher the brightness level
bone signal, especially the shorter
he cuts off a part from the “saw”, which leads
to a change in duty cycle (ratio of duration
values of zero and unit levels)
output signal of the DA1 microcircuit, and the sign
cheat, and the brightness of the corresponding area on
computer screen. Availability of C10 elements
and R18 allows you to change the contrast of the image
fermentation. Signal swing at input 4 DA1
installed by selecting resistor R9. On
elements DD9.1, DD9.2 assembled low-pass filter
high frequencies, highlighting frame synchronization
pulses from the synchro mixture.
DIGITIZER SETTINGUP
===================
Setup should start with analog
parts, because before the advent of personnel synchronization
pulses (KSI) on the third pin of DDCh.1 and
sync mixture (SYN) on the third pin DDЗ.1
The digital part cannot work. For na-
fix this part of the circuit to connect the board to
the computer is not necessary.
The VIDEO input is connected to the video output
TV detector directly or (if
strong reception interference) through the emitter
(source) repeater, similar to the cas-
kadu on VT2, R5, R6.Quality of operation of the amplitude selector
depends on the signal level at the collector
VT1, which is regulated by resistor R3.
Achieve clear KSI and SYN, and then sub-
use R9 drill to set the signal amplitude to
4th pin DA1, approximately equal to the amplitude
de on the 3rd pin of this microcircuit (2/3V).
To check the digital part of the circuit, replace
press button K1. Check availability of all
output signals: signal on the 3rd pin
DA1 and the first pin DD12, make sure that
the BUSRQ signal is connected to the 25th pin of the pro-
tsessora. The DOS signal is generated from the con- board
drive troller (low level sign
waits for the controller to turn on), but you can
just short the 13th pin of DD7.4 to +5V.
Now smoothly adjust resistor R18
until the image appears on the screen. Regu-
polar repetition of identical parts iso-
fermentation probably means the closure of hell
res anywhere on the digitizer, starting
from the meters. Periodic interference, appearing
appearing in the picture requires more precise
selection of capacitor C11 or inverter
testing of the 7 MHz signal.
Resistors R12, R16, R17 can be replaced
jumpers. Instead of K555 series chips
you can use similar microcircuits
K1533 series without restrictions. To eliminate
indication of possible self-excitation of the microcircuit
K554 SAZ is recommended to be closed between the
fight conclusions 7 and 8. Betweenpower buses
preferably evenly over the board area
install at least four capacitors
with a capacity of 47 nF...1.0 µF. Connector layout
Ma X1 digitizer is completely identical
computer system connector wiring
Leningrad-2.
Pin 5 of the D11 chip is best not
solder to the board (bend it) and connect
it with pin 2 of the same microcircuit. Necessary
one jumper is required between the first pin
house D14 and the eighth pin D6. Between IORQ
and +5V, install a 1/3 kOhm resistor.
PARTS LIST
==============
You can use microcircuits of any se-
ria 555 or 1533. Parts used:
X1 - SNP-64
R1,R2,R6,R7,R13,R19 - 1K
R3,R18 -22K
R4,R10,R11 - 240
R5,R14,R15 - 10K
R8 - 100K
R9,R20,R21,R22 - 3K
R12,R16,R17 - 0...27
C1, C2, C4, C8 - 1.0
C3 - 33N
C5 - 100
C6 - 47.0
C7 - 6H8C9 - 1H5
C10 - 0.1
C11 - 470
DD1...DD2 - K5SSUE19
DDЗ...DDS - K5SSTM2
DDb - K5SSLL1
DD7 - K5SSLI1
DD8 - K555LAZ
DD9 - K5SSLE1
DD10 - K5SSLPS
DD11 - K5SSLP8
DD12,13 - K5SSUP16
DD14 - K5SSUP23
DD15,16 - K5SSUP22
DA1 - K55CHSAZ
VT1...VT4 - KTZ15G
PRACTICE
========
Several dozen copies of digital
tasers were successfully connected to all
popular variants "ZX-Spectrum" with a common
memory field. In all cases the device
showed good performance and stabilization
stability of parameters as when working with temperature
cameras and video recorders, as well as with
all TV models.
PROGRAMMING
================
Readers who know assembly language can
write complex programs yourself
we, who, for example, will be able to remember
and play entire segments of TV shows
dachas both on the entire frame and on 1/16 screen -
on. For example, a program in BASIC, which
which performs viewing on the screen of your
your computer television broadcast and
recording the selected frame to disk:
10 INPUT "Filename:"; A$: REM enter name
file
20 OUT 247.0: PAUSE 0: REM recording
one frame in RAM
30 IF CODE INKEY$ <> 32 THEN GO TO 20:
REM if you press the spacebar, then the program
will be written to disk; any other key -
preview next frame
40 RANDOMIZE USR 15619: REM: SAVE A$
CODE 16384.6144
50 GO TO 10
DIGITIZER DIAGRAM
===
Nah, not so fast... Uh-uh,it's already
not V.M.G., but Max is the editor of the magazine. to me
Well, it’s a pity, but such laziness attacked the scheme
draw, given its size, what are you
forgive me generously... If anyone needs it,
then I can send you a photocopy of the diagram for
a certain fee. The fee is purely symbolic
cheskaya - a photocopy of the sheet costs 20 kopecks
and the envelope in Ukraine is currently 45
kopecks In short, for residents of Ukraine the scheme will be
children cost 1 hryvnia, and for everyone else -
to customers - 30 US cents. In the letter with the order-
please send a receipt for the transfer (for
Russia) or send 1 hryvnia in the same
message, but in such a way that it doesn’t come to light
glowed. Even shorter - no money - no
schemes! No receipt - I'll wait for arrival
money, and this is about a month from Russia. On-
example, the transfer came from the Kursk region 1
month exactly. I can imagine how much it will be
go from the Urals...
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