╔════════════════════════ ═══════════════════ ═══════════════════╗ ║ CDOS modem. ║ ╙─────────────────────────────── ───────────────────────────────╜ (C) EVP-SOFT Improvements to the CDOS modem to improve communication. Hello everyone. To begin with, I want to express my deep gratitude to ityKPN'y for providing quality improvement material transmission (item 1) and reception (item 2). All the information below has been tested on both of my modes - max ("ROBERT" and "FARAON") with very positive results. The first part of clause 6 mainly applies only to the "ROBERT" modem, and On the "FARAON" modem this replacement has already been made. Test Modem V2.01 (MT_2.01) will be released soon - it allows you to evaluate the degree of adjustment of the D7 bit; for CDOS this is not important but, for EMS and MMD the bit must be configured, i.e. with long and short beeps, the number of 1s must be equal to the number of 0s per short periods of time (1/50 sec.). 1.Improving transmission quality. Thanks to EVP SOFT's advice, I experimented with resistive rum, which stands between the "-" tel. lines andoutput collector transistor. Usually a resistor from 430 Ohm to 640 Ohm was placed there, at different different modems - in different ways, but the optimal one (for my line) turns out to be 390 Ohm was detected, further reduction of its nominal value only worsened lo connection. The point is most likely that with a small value of the resistor on surges appear at the fronts and falls of pulses, noticeably worsening connection (the modem can recognize them as additional names pulses). Therefore, short-circuiting it, as some advise, is not worth it. And with a large value, the signal is greatly weakened. In general, experiment with this resistor and select him under his line. Finding this resistor is easy; it is located between two trans- resistors located next to the connector. 2. Improved reception quality. On the advice of FARAON, I paid attention to the electrolytic The capacitor standing next to the transformer was dead. But I went further - I increased its capacity to 47 µF. Quality the reception increased, but I was not satisfied with this. I noticed to a resistor that shunts the primary winding of the transformer, such the feeling that it was installed “from a flashlight”, from 470 Ohm to 1 kOhm, but from the quality of communication depends very much on it, for example, only due to For many, EMS does not dial the number (i.e. bit D7 does not work). I had to go the simplest route:replace it with trimmer resistor 1OkOhm and catch the best connection manually, but the results exceeded all expectations - the quality improved dramatically reception, there was a connection with BBS, with which there was no connection before lo connect. This resistor is closest to the transformer and one of its the output is connected to "+" replacing its electrolytic capacitor ra. 3. Installation of the 5th LED. Moscow CDOS modems initially have 4 LEDs, "receive" - indicates that there is some signal on the line, "transmit" - shows that the modem is transmitting something, "tube up" - if the modem picks up the phone, and “ring” is a call to the PBX, however, what the modem dials the number - it is not displayed, so some kind of be the program can dial the number unnoticed. To exclude this, you need to install a "dial" LED. And this LED is placed between +5V (you can take it from pin 16 TM8) and 11 pins of the same microcircuit. If everything is correct and the LED is working properly, then it lights up after dial in BASIC "OUT 239.64". 4.Replacement of LEDs. It only makes sense if the appearance of your computer is not for you indifferent. Well, in general, the "receive", "transmit" and "dial" LEDs can be any imported - for example LDХО5, LDЧO4, LDЧ15, LDЧ14 and many others - current consumptionIt doesn't matter much. But the “tube up” LED must be changed carefully, because he's standing in the transistor circuit, and the voltage in the body depends on it. lines when the phone is off-hook. Therefore, before replacing it, you need to remove it demo the tube and measure the voltage in the phone. lines. This may change thread reception/transmission quality, but in an unknown direction. I don’t know about “ring”, but experiments with it may lead to to the fact that the microcircuit in its circuit will burn out (it seems LP12, but not is correct). However, I have had LDCHO5 for a year now. The brightness of the "receive" LED can be increased if tantalum The first 1 µF capacitor (it is located next to the LL1 microcircuit) is placed hire at ZmkF. This does not affect the reception quality. 5. "MODEM RESET" button. Very useful, for example, in CDOS you can hang up without getting through different menus to "TUBE UP/DOWN", and in ISDOS - There is no need to clog up your memory with the resident "trubka.res" which It takes up more than 300 bytes and is still buggy. In addition, it can also be interrogated programmatically, for this purpose: before when writing to the modem port in the data byte always set 4th bit, and then read its state from the 5th bit, and if the 5th The bit is cleared, then the button is pressed. For example: MDRES LD A,(MDRES1) ; there is the status of the handset and other modem keys OR #10 ; write "1" to bit D4 OUT(#EF),A NOP; delay, but not necessary IN A,(#EF) ; we read AND #20 ; check bit D5 JP Z pressed JP not pressed Installing this button is very simple. It is placed between 8 and 1 pins of the TM8 microcircuit. In this case, it is necessary to break the "RESET" signal going to the modem from the computer, and solder the KDS21 diode into the wire gap, key to the modem. If the polarity of the diode is incorrect, pressing pressing the button will lead to a general RESET. 6. Setting up the comparator. First, check the two electrolytic capacitors that These are located at the end of the LL1 and LP8 microcircuits. Over time they may get hooked. If there are 47 uF capacitors, then replace them with 100 μF - this will improve the purity of reception. Secondly, next to the pair of capacitors mentioned above there is two 1 kOhm resistors. If you place the modem with the connector facing you, then one will be symmetrically behind a pair of capacitors, and the second on the right. Instead, you need to install a tuning resistor (preferably multi- go-turn, or large variable type SP-I) at 1.5 - 2.0 kOhm. And with its help you can adjust the comparator, all you need to do is configure it once, but for more precise settings you need to use non- how many subscribers? Thirdly, the comparator is affected by the installation of a ceramic con- 0.1 µF capacitor between 13 and 4pins of the UD2 microcircuit. He affects signal stability. But in general, with the right it is unnecessary for setup according to point 1. 8. Assignment of CDOS modem bits. When writing to the modem: D7 - transmitting key, its state is the "transmit" LED; D6 - numbers dial key, for visual observation of it status, you need to set the “dial” LED (see point 3); D5 - pick up the handset, if the phone is picked up and there is a line, it lights up "tube up" LED; D4 is a bit that is written here and can then be read from D5, this is used to check the presence of a modem, search for it and for polling the "MODEM RESET" button; D3...D0 - not used. When reading from a modem: D7 - comparator output configured for PBX signals (for example, short beeps). If it is not configured, then MMD and EMS are not set They call the number and do not respond to short beeps. D6 - reset to "0" at the time of calling the PBX. Reset this bit accompanied by the lighting of the "ring" LED; D5 - see D4 when writing to the port; D4 - comparator output configured for signals from another modem; D3...D0 - not used.
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