Laboratory - CDOS modem of the "Alegro" type for ZX-Spectrum compatible computers.

        CDOS-MODEM TYPE "ALLEGRO"
 FOR ZX-SPECTRUM-compatible computers
        Version by SSSR'99, Gomel
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(C) KVAZAR
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   I present to your attention the modem circuit -
new adapter for ZX-SPECTRUM-128 and higher.
It is a recycled and
modified version of the Minsk scheme
by ARS, but unlike the latter,
gives a number of significant differences and advantages
instv:
   - complete galvanic isolation from the
lephone line;
   - new comparator circuit, as a result -
those of which, communication has noticeably improved;
   - automatic blocking has been introduced
signal IORQGE, now connect the modem to
computers with left port decryption
external devices does not amount to much
labor;
   - automatic reset of the modem when
Press RESET (the modem hangs up).
   - the number of chip packages has been reduced,
more rational layout, which allows
it was necessary to halve the dimensions of the printing
no modem board.
   - LED indication of busy modes
line, reception and transmission (installation
at the request of the user);

   Software support: all versions of ter-
terminals EMS, MMD with redesigned driver
modem rom, games GAMBIT (chess), "Mors-
what a fight."This version of the modem is completely
compatible with Minsk and Moscow variants
tami.

   Let's move on to the description of the fundamental
diagrams (see picture in the appendix to the newspaper).
ATTENTION!  All values of resistors and con-
densators are given in relation to Gomel
telephone lines and our PBX, so we
Most likely, in your case you will have to
find specific denominations yourself
(focusing on the quality of communication)!
   Name of elements:

      D1 - K5SSTM8 VT1 - KTZb1
      D2 - K5SSЛЛ1 VT2 - KT815
      D3 - K5SSLP8 VTZ - KTZ15
      D4 - K55ChSAZ VCH - KTZ15

   All diodes are KDS22.
   Resistors such as MLT or similar.
   Capacitors of any rating.
   Any transformer, small-sized with
three windings 500, 250 and 250 turns, with
output from the midpoint (such trances
can be found in rotary telephones
tah).
   Relay - RES-10 with 12V power supply. Unlike
from the five-volt RES-49, previously located in
Minsk scheme, it is more accessible.

   Built on a K5SSTM8 trigger chip
recording port.   On K5SSLP8 - read port, and
on K5SSLL1 - decoder.
   Microcircuit K55ChCAZ - comparator.  Diodes
in the circuit of the fourth output of the comparator, the
This is the threshold signal level.

   The modem is connected to the ZX-SPECTRUM bus,
according to the signals indicated on the diagram. Sig-
cashIQGE is nothing more than an IORQGE signal.
The signal RESET can be taken both from the bus and
and from the "reset" button. Installation should be carried out
use thick enough wires, mini-
short length.
   To properly configure the comparator
modem to a specific telephone line
An oscilloscope is required. Controlling
level and shape of the signal in the line, selecting
resistors and capacitors in the 4th pin circuit
yes K55ЧСАЗ, should achieve stable performance
modem bots on most intracity
PBX at 2400 Baud using pro-
EMS 2.55 and driver no lower than 4.02.
   About ports.  The modem has three standard
connection ports: #EF, #F3 and #77.  Scheme
The modem has automatic blocking
external devices (see Polesie-13), but in
a number of particularly severe cases may require
try to tighten up the decryption).
   About the line. Before connecting the modem, please
measure the voltage in the telephone line.  When
with the tube down, it should be about 60
volts, and when raised - in the range of 7-15V.

   For all questions related to assembling and configuring the modem,
contact the newspaper editor or directly the developer
schemes: (0232) 50-31-61 Alexander /SSSR/.