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I'm thinking about an unique one to benefit from the strenghts of the platform, although porting something first to test the grounds is likely. Almost anything can be ported, if it does not take up much RAM (like ZX-7 and ZX-16) - there is plenty of ROM to hold a ton of song data, and CPU speed is a bit faster.

Actually, as I still have troubles with 8253 emulation and other things take priority at the moment, porting an engine or a few is a good next step.

Modding and testing the hardware

Finally got a ZIF 28-pin socket ($3.4, with quick delivery) and ten Winbond W27C512 DIP28 Flash ROMs ($6.2) from China. The latter is just in case, of course I don't really need that many. Anyways, it now become possible to finish my modifications to the AON unit I'm going to use to occasionally test my software during developing, as well as finishing the emulator - this means relatively frequent tests, and modifications were made to make this process more comfortable. Let's see what has been done. Please note that most of the modifications is only needed to develop software more conviently. You don't really need most of them in order to just use it once its done.

First, I fixed everything inside the case, using tons of hot glue - just like it has been done in 90s.

I added socket for phone handset, to make it detachable. Also added phone line and power source sockets. The power source is now USB Type B, this allows to use any USB phone charger supply, which is really handy, or a power bank - so it is a portable now. As much portable as a regular brick. There is Reset button added that is normally not presented, but useful to do tests.

As I need relatively frequent tests, I decided to use ZIF socket, because normal ROM socket wouldn't provide reliable contact, relatively difficult to connect/disconenct, and would wear out soon. The length of ZIF socket pins and other parts on the board not allowed it to fit into ROM socket directly, so I used yet another ROM socket in between, plugged them into each other like a tower. Not really physically reliable, but it works if used carefully.

I did a hole in the bottom of the phone body to expose ZIF socket for easy Flash ROM replacement. It is a bit too tall, not allowing the phone to stand on a flat surface as it normally should. Thus I added front legs extender, that raises the front part of the body, adding missing height. Not pretty, but does the trick.

I flashed the PHON-LP2 test ROM I mentioned above using WizardProg-87 - all smooth and easy, no issues. A very handy inexpensive piece of Chinese gear, if you happen to burn ROMs time to time. As it is a 512K Flash, but AON only supports 32K, and the test itself is just 2K, I simply copied these 2K all across the 512K image using a HEX editor, to avoid cutting/grounding chip legs (extra address lines). The test worked just fine. I learned how it behaves on this particular board (no 8253 RD, no configuration diodes), and that it plays clicks and short music phrases during testing - good to know in order to make emulator work correctly.

Here is a video of the unit running the test: https://youtu.be/rR_g8js13oY

Flashing the test ROM with the WizardProg-87 burner.

Inside of the test unit. Now with extra two sticks of hot glue.

Close up of the ZIF socket. It just plugged into a regular socket then into the board, not physically fixed (yet).

Newly added reset button on the left, USB Type B socket for the power and phone line socket (just in case I need it for something) on the right.

Phone body with bottom part screwed into its place. Extended legs at the front.

With a Xiaomi power bank now it makes a fully portable Z80 micro computer.

Hardware review #5

While I'm struggling with proper 8253 emulation, yet another item of curiosity I got for $7. This is one of the latest AONs built on the custom 8051-based R100-XP MCU, one with on-die AY-3-8910 clone.

As it is one of the latest devices of the era, made circa 2003, build quality is relatively high, and overall it looks more like a properly made consumer product rather than a half-DIY half enthusiast thing. The phone case and buttons has labels in Russian, there is a good packaging box, and a very detailed manual, all in russian too. The board inside called Venus 5, latest of that family. Besides the R100-XP there is not much parts on the board - LED driver, 24LC16 Flash, the main 512K ROM, and a bunch of amplifiers.

The ROM is in fact Flash (EN29LV040 in my unit), mounted into a socket, so it can be modded very easily - if you happen to have a ROM burner with 32-pin PLCC adapter around.

My unit has Rus-28 Sonata firmware, instead of the AY music it features 'MIDI polyphony', as it called in an official schematics book. But there is no dedicated MIDI synth chip on the board, and schematics is barely different from the AY revision (just a few resistors and capacitors). The offical docs from the maker of the Venus boards mention that since build 5713 of the firmware it has a 6-channel MIDI Wavetable Synthesiser, so it seems to be a software synth. As the AY clone is part of the custom MCU, it should be easily usable no matter what board and firmware it is, but the MIDI synth has to be somehow hacked out of the original firmware if someone would like to have it.

The MCU also has a 8-bit DAC, so the firmware features relatively smooth volume control for all sounds.

The packaging box and manual.

External view.

Keyboard close-up. The russian labels done in the cheapest way, but at least you can now have idea what the extra buttons doing, plus there is marks on the case itself for the calculator layout.

Internal view. not much is in there. Unlike all other phones in these reviews, all boards now custom made, and the battery backup pack wires is actually connected to the board.

Back side of the PCB. 512K Flash ROM is on the left.

Front side of the PCB. The R100-XP MCU is on the right. Sorry, the mark is so weak there I couldn't catch it to be visible on camera.

Logging format has been changed a little bit, more formats added, and whole exporting thing is impoved in general. For one, you can export specified part of the song, or the whole song, without need to cut out the silence inbeginning and end, by marking beginning and end of exporting area with any change for controllers 20 (begin) and 21 (end).

Test ROMs

Since beginning of this thread, I was slowly working on the emulator that was abandoned since 2014. It is a must to develop new firmware efficiently, also a great help to figure out details about the architecture that remain unclear due to mistakes and difference in various schematics available, such as memory and I/O maps, keypad matrix layout, and so on. Now, when it starts to taking shape (more on it later), there is something different than the flood of HW reviews to share.

Due to the nature of the platform that was almost like DIY in early years, and due to the way parts were sold in 90s, Z80 boards nearly always has a ROM socket installed (sometimes CPU and other large chips too). As neither parts nor boards were of a great quality, it often was tricky to make the thing work once you assembled it. Thus there was a number of test ROMs from different authors that can test the hardware all the way through, helping you to figure out lots of potential issues ranging from faulty chips to missing connections or short circuits easily. It is a great help in making emulator too, in fact it was a huge help to me. There is normally no such a luxury with emulator development for other platforms, even popular ones.

Test I'm using the most called PHON-LP2.ROM, from 1995. It is one of latest and most complete, judging by the very detailed doc provided with it. It is just 2K, so you can save the 8K ROM banking headache for later. The doc is of course in Russian, so I give just a brief outline of its functionality.

In order to run it requires bare minimum of properly working hardware in order to start, namely no short circuits in CPU address, data, and control lines, correct clock - in other words, functioning CPU.

First it tries to check 8255. If there is some problem with it or related parts (listed in the doc), it shows error message using single digit of the display, as multiplexed display is not possible without these parts working correctly.

Then it tests LED display and multiplexed display circuit that is also used to poll the keypad matrix, by showing each digit with all segments on, then segment by segment. You can visually see if there is something wrong and get leads to possible source of the issues. From now on test displays pseudo-text messages that specify detected issues.

Then RAM gets tested, 6116 and 6164 supported and detected automatically. At this point test can detect missing CS, RAM degradation, and other memory faults.

Test also checks if the data bus pull up resistor array installed, some firmware versions won't function correctly without it, although some makers were omiting it to reduce the costs.

8253 gets tested next. Issues with control signals, lack of RD signal can be detected. Then 8253-generated interrupt gets tested, so you can see if interrupts is not working.

Test also checks optional configuration diodes (kind of jumpers) that enable expanded keypad and other options in some firmware. I'm stuck at this part at the moment.

A dozen of other hardware checks performed then, ones that related to the analog part, such as if phone line is not connected, incoming call detection, and so one.

Finally you can test the keypad, either normal 12 button one, or expanded 24/32 buttons - press buttons, and corresponding LED segments will light up. Turned out to be extremely handy, considering a bit tricky matrix layout and multiplexing shared with the display, plus two different layouts for normal and extended keypads.

If this is still not enough, you can then go into 8255 direct control mode. It allows to enable/disable any output line using the keypad, to help you make further HW checks manually.

Hardware review #3

This device is not to be used in the project, got it for $6 just out of curiosity, as I've seen a lot of similar devices in the same exact case, but with different names and marks. Turned to be very interesting indeed. An add-on AON unit called Lart-201p from December 2002, compact design of the end of era.

A very small device, can be powered from the wall adapter or 3 AA batteries, has the usual 80C31 architecture (for the most part), quite good speaker, and a cut down version of the usual Rus firmware. Actually could easily be a totally portable 1-bit music box or something, but unfortunately this late design uses all SMD parts, the ROM is one-time programmable and has no socket. The parts now is all Chinese imports - by the time it became much more accessible and cheaper, so not a single Soviet made part there.

The most fun and major difference in this particular version of architecture is that it uses serial Flash memory chip 24C16 (2Kx8) instead of the usual 6116 SRAM. As the device functionality does not suppose very frequent information changes (incoming calls list, phone book), it neiter needs much speed nor too many write cycles. Although the endurace of the chip is 1M cycles and it supposed to last really long, there were talks that the modified firmware works very inefficiently and doing lots of unnecessary writes, so the chip got worn out after 2 years of normal use, and had to be replaced.

External view.

Back side, the AA batteries compartment is there.

The inside, it has three boards - the main one, 5-button keypad one, and sockets one (not seen on the photo).

The main board with the main chips marked.

Close up on the 80C32 and 24C16. Small chip on the bottom left is sound amplifier.

Finally the large display. You can see it often in 80C31 designs.

Regarding the UV EPROMs. As far as i know, Soviet electronics production only managed to get 8K done with reasonable yield. To my knowledge, no UV ROM chips has been released with 16K or more - anything of this capacity in Soviet stuff were mask ROMs or imports. For things like ZX clones Z80 and ROMs had to be imported, and that was very difficult at first. Thus in early stuff such as first ZX clones you can see either 8 of 2K UV ROMs or 2 8K UV ROMs to get the required 16K. Later importing get easier, but prices on local made components were still lower, so in early post-Soviet things like AONs you'll likely will find cloned CPU (sometimes original, though), but ROMs always will be imported. Spectrums were made in large quantities, so a mask ROM with Didactic Scalica firmware was made and used eventually, but AONs were product of individuals and small groups, so it always remained to be using UV EPROM.

The sound

One interesting topic to discuss is what has been done already in regards to the sound in these devices. Music was relatively important there, used as ring and alarm tones. At first it was all monophonic 8253-driven square wave, as you could hear in the videos linked above, but later (past Z80) designs actually got polyphony and better sound.

At first the sounds range that AONs were capable of consisted of:

- Single channel sound cues and melodies
- One bit voice samples
- DTMF signals for tone dial

As far as I know, no one tried to do 1-bit synthesis for more complex music timbres and/or polyphony on the original hardware, although you can be sure a lot could be achieved there (and that's the goal of my project), especially considering hardware PWM possibility.

With the advent of 80C31 based AONs, sound started get more advanced. At first it was still one channel square wave, but with arpeggios and stuff (Rus 27). I think the CPU power of 80C31 at 10-12 MHz is roughly equivalent to Z80 at 4 MHz, maybe a bit better, but totally different architecture creates an interesting field for experiments with 1-bit synthesis.

Now, if you somehow get tired of 1-bit and want to try something different, there is more worth to mention.

Circa 2003 people from the Rus firmware devs, now turned into Rus Telecom company, managed to get 80C51-based MCU ASIC into production at Taiwan, called R100-XP. It has been designed specifically to be used in their AONs, with most of required interfaces built-in, and the most interesting feature of it was on-die AY-3-8910 replica. Phones based on this MCU, like Rus 28 Sonata, actually contained 1990s ZX Spectrum demoscene music! It sounds just like the real thing. Unfortunately, these phones are kind of rarity and hard to obtain, as they were produced and sold at decline of the AONs popularity.

There is another Rus 28 Sonata phone as well, likely with different board revision yet the same basic firmware, that besides the AY replica has 6 channel polyphonic music with more complex timbres. I don't have much info on this, but it sounds on par with the early polyphonic cell phones, and the sound is likely produced by some MIDI chip. Maybe VS1033 (was popular back then) or something.

Nostalgic things

There is also a personal retro computing nostalgic factor that may feel kind of weird for you, but still. Back in the 1980s electronics and computer related stuff in USSR mostly were both rarity and luxury. People weren't yet much familiar to home computers, electronic games, video recorders, TVs with remote, FM radios, and such, it all was a technological novelty coming directly from foreign movies and sci-fi books. In the very late 80s these things started to get imported and appear on the black market under insane prices, and with the fall of USSR all kinds of imported and local built electronics flooded the country - you probably have heard of Spectrum clones and Dendy, as few examples of this.

For us kids of the time all kinds of previously unseen technology were extremely fascinating. Casio watches with melodies, Chinese sound effect keychains, Game&Watch clones, Brick Game (Tetris electronic game) - everything caught our curiosity and attention. We loved to explore its capabilities, disassemble it to see what is inside, and so on. AONs became part of this too. Besides the ever-fascinating clever use of the 7-segment LED display that used to produce cryptic text messages (Ln Hold), one thing we appreciated a lot was the sound. Right from the excerpt from the Mikhail Glinka's 'Glory' that played during power up sequence of the Rus firmware (originally a choir piece that sings 'Glory to Russia', akin to the firmware name that is short for Russia), to a few dozens of built-in ring tones and alarm melodies, which were versions of classical and popular music. We listened and loved to recognize the famous songs in this basic square tone computer renditions. As you may guess, with Z80 and 8253 on board it was all monophonic 1-bit square wave music, albeit nicely programmed. One missing historic piece that alongside the Speccy and NES music got many of us here interested in computer music in general.

A bit later the Rus firmware was upgraded with speech synthesis - male then female voice that could say the incoming call phone number, or current time, and some other things, constructed of pre-recorded words, like old talking clocks did. It also could be used to know who was calling when you're not at home, you could call to your own number and use tone dial phone (or portable DTMF beeper device even!) to enter password and hear the speech synthesizer talking you through the call list. It was very impressive at every level, and voice quality was pretty nice for the time. Think of how voice clips were impressive in early computer games.

Close friend of mine at the time (mid 1990s) was involved into production of AONs, his father ran that private business, so he helped with soldering and assembling a ton of them. Thanks to this I learned a lot about the internals, and was also fixing and upgrading AONs for my friends time to time. So it provided me with some early digital electronics skills.

I first got the idea to use the hardware to produce some sounds back in 2014, when I was thinking of creating a simple 1-bit DIY synth and was considering to use Z80. I thought I still owned a pair of old AONs that used to belong to my childhood friends in 90s, and did some research, planning, and programming of basic emulator to make further development more comfortable, with plans to create a simple 1-bit programmable drum machine out of it at first, and something more interesing eventually. Unfortunately, later it turned out both of these somehow went to trash during major cleanup at house at some point in 2013, and I havent't found another one. Then other stuff got priority, so I had to postpone the idea. Until now!

You can listen to some of the monophonic music here: https://www.youtube.com/watch?v=A0IKdIRfoFw. This is Rus-25 on the 80C31-based board, but the same music was in the Z80 version as well (Rus firmware went to 23rd revision there, then moved to the new HW).

You can hear the speech synthesiser in this boring and shaky video, as well as see some of the interface. Again some of 80C31-based versions. https://www.youtube.com/watch?v=SOHX96BbhCk

It will work, but basically it just inverts the idea of playing sound in spare CPU time that is left of a frame - the second apporoach I described above. Just different technical implementation.

Engines like Special FX work better with this approach, because of very short pins they're generating.

Seen interesting comment on youtube recently where a guy explained his understanding of how Wham and other interleaving engines works. It is interesting way to look at the things. He considers that logic of such engines is:

- when both channels has output 0, engine outputs 0 to speaker, thus output weight is 0
- when both channels has output 1, engine outputs 1 to speaker, thus output weight is 1
- when channels output is not the same, engine outputs sequence of 1 and 0 at it maximum possible sample rate, which makes kind of output weight 0.5

No, I wasn't able to figure out clicks. You can hear it just by using the third channel, any notes, it is quite apparent.