Hardware - VICOMM - compatible modem from MSD group.

          VICOMM is a compatible modem from MSD group.


TDD/MSD 2000


     Perhaps you have already seen the circuit diagrams of VICOMM can-
demos developed by other people. Our scheme is different from
most of them with some parameters:
     - complete electrical isolation from the telephone line;
     - absence of a low-tech transformer;
     - digital inputs and outputs to circuits;
     - circuit-unlimited transmission speed.
The decoupling is made using optocouplers and is used as optocouplers
assembly AOD109A, this assembly contains three sa-
independent optocouplers. In the diagram they are designated as separate
diodes, numbers indicate terminal numbers. Micro-assembly AOD109A
assembled in a planar package with a pin pitch of 1.25 mm therefore
soldered from the side of the tracks. The key is the thickening at the base
first output.
     Our modem requires digital inputs and outputs because... this is
expands the possibilities of using the modem (in the future it is possible
connection to your port (on the system bus) and, possibly,
to a hardware data compressor...
     This feature of our device somewhat complicates
connection, but improves modem performance. Used in the modem
quite sensitive reception amplifier, based on it
a comparator has been made, which significantly improves the quality of reception
data.

Signals used by the modem:
   MANAGEMENT - thisthe signal controls line seizure,
1-line is busy; 0-line is free. With this signal
You can programmatically seize/reset the line and dial a number
(more on this below).
 IN - this wire sends data to the modem for transmission.
 OUT - received data goes through this wire from the modem.


 Description of the circuit operation:
   When applying log.1 to the input of the control unit. LED lights up, indicator
seizing the line, then this signal is sent to
logic elements DD2.3 and DD2.4. To other inputs of these elements
the IN signal is received, direct to DD2.3, inverted to DD2.4
ated by element DD2.1. At the same time, at the output of one of these elements
Log.0 appears, supplying power to the LEDs of optocouplers, when
IN=0 - at output DD2.4, at IN=1 - at output DD2.3. At the same time
different current flows through the LEDs, depending on the state
signal IN, changing the brightness of their glow and the current through the fo-
LEDs respectively.
   Next, the emf induced on photodiodes V10, V11 opens the key
on transistors VT12, VT13, depending on the current through the fo-
LEDs either completely or partially. Fully open
key, the line drops to 12V (set by resistors R11,
R12), and if incomplete - up to 20V (set by resistor R8). Di-
one bridge is needed to connect to a line of any polarity
yu.
   Receiver: Current flowing through the line, modulated
a useful signal also flows through LED V9. Which os-
broadcast by photodiode V6, the current through whichrepeats the current in the line.
The variable component is supplied to the
amplifier DA1.1, where it is amplified and fed to the comparator
DA1.2, where it is converted into digital form. Resistor R6
set the comparator response threshold. Further signal through
the DD2.2 inverter is supplied to the output of the circuit.

 Now about dialing:
 The graph shows a set of numbers 3 and 2.


 U│
  │<-t1-> <--t2---> t3 t4 <--t5-->
U1├───────┐ ┌──┐ ┌──┐ ┌──┐ ┌──┐ ┌──┐
  │ │ │ │ │ │ │ │ │ │ │ │
  │ │ │ │ │ │ │ │ │ │ │ │
U2│ └─────────┘ └─┘ └─┘ └────────┘ └─┘ └───────
  └──────────────────────────── ───────────────────────────>t


When the handset is on the phone (t1) the line voltage (u1) is 60
volts When the tube is removed (t2), the voltage (u2) drops to
approximately 15 volts and the station gives a long beep into the line (at
approximately 500 Hz), this is the signal that the station is ready to dial. Set
produced by shutdown pulses (t3) with a duration of 60
milliseconds and connection pauses (t4) lasting 40 milliseconds
liseconds (period is 100 milliseconds). Between the numbers there is
interdigital pauses (t5) with a duration of 400...10000 millises
kund. The number of pulses corresponds to the dialed number (zero
corresponds to 10 pulses).

    For connection information, see the file picture innewspaper supplement. Circuit diagram and printed circuit board
modem, as well as drawings for remaking the Scorpio board
are located there. To connect, it is necessary to modify the circuit board
you, but keep in mind that after remaking the board it will be impossible
use a tape recorder to load and unload.
    In Fig. 1 (top view of the board), two are marked in red
capacitor and resistor that need to be removed.
    In Fig. 2 (bottom view) the track you need is marked
cut, and the dotted lines indicate the necessary connections.
    After the modification, all signals can be taken directly from the peripheral
line connector. Let me remind you of the necessary conclusions:
 IN - 24 on top, OUT - 24 on bottom, +5v - 20.21, ┴ Ground -1.30.
An unused pin was taken for the CONTROL signal
connector - 8 from the bottom. It is needed so that the modem can pick up and put down
handset, and also dial the number. For program access
This is bit D5 of port #FE (254). In the future, we intend to support
keep this feature in programs.



                Description of the operating principle and author of the TDD modem.
             Editing, proofreading and additions by Pink Panther.
Assembly and debugging of the BETA version with the Pink Panther PCB.
                                      MAX SNAKE fix.



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