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Creative Music System (CMS) / Game Blaster compatible replica

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    Creative Music System (CMS) / Game Blaster compatible replica


    I read about Creative Music System (CMS) / Game Blaster at Great Hierophant blog. This sound card based on two Philips SAA1099 chips and looks easy to duplicate. Easier than adlib: SAA1099 data lines to ISA data lines, A0 to ISA A0, Vref through 10K resistor to VCC, DTACK (open collector output) not used and pull-up with 10K to VCC, CLK from ISA-OSC divided by two by 74ls74 or another counter. First SAA1099 chip CS to address decoder 0x220 and second SAA1099 chip to address decoder 0x222. Thats all!

    But the most difficult - card autodetect. Great Hierophant write:
    The left SAA-1099 is at I/O 2x0 & 2x1 and the right SAA-1099 is at I/O 2x2 & 2x3. The subsequent twelve I/O addresses are used by the CT-1302. For a long time, the function of this chip was a mystery, but now we know what it can do. One problem which Creative used this chip to solve was that of detection. While the game publisher could require a user to tell a program the hardware he had in his system, it would be difficult for a less savvy user to know or remember what he had or where in the I/O space it was. Creative decided to make it easy for the consumer and the game programmers by allowing the card to be detected by software.

    In order for a card to be detectable in software in a PC, it has to give a reliable, non-random response to a read from the processor. The SAA-1099s cannot be read, only written, so there was no reliable way to detect these chips in software. Here is where the CT-1302 comes in. For the remaining addresses, 2x4-2xF, it will store or latch an 8-bit value written to it in one register, which is then read back by a program from a different register. If the values written and read match, then the card has been detected successfully. If they do not match, then the card is not detected. There must be two different I/O addresses involved, otherwise this scheme does not work reliably.
    I tried to emulate this method in emulator - data written to 0x224-0x22F port is stored to variable and then read back when access to 0x224-0x22F port, but some programs did not detect card. Then I looked at the source code of DosBox and I found this logic: data store only when 0x226 or 0x227 port write. Other port ignored. Data read back only if access to 0x22a or 0x22b port. Other port ignored. And last thing - when reading port 0x224, data allways must contain 0x7F:

    PHP Code:
    uint8_t cms_port_read(uint16_t addrvoid *p)
    uint8_t res;
    addr-0x220) {
    res 0x7f;
    res lastwrite;

    void cms_port_write(uint16_t addruint8_t valvoid *p)
    addr-0x220) {
    lastwrite val;

    So, we need RAM to store 1 byte. I think i can use latch register. And i am looking the best way to do the decoder... Original card used 74ls138 2 pcs and 74ls139 1 pcs. At first approximation my circuit:

    /IOCS16 not used, this must be AEN signal..

    Any ideas or suggestions?

    Should be simple to do with a small CPLD or even a couple of GALs, no? For a one-byte memory TI/MMI made some LSTTL that looks like an LS374, but has read-back capabilities (74LS793/794), but those would be pretty hard to find now. TI also had some octal bidirectional bus registers (74LS651-4), but again, probably hard to find.
    Reach me: vcfblackhole _at_ protonmail dot com.


      Originally posted by Chuck(G) View Post
      Should be simple to do with a small CPLD or even a couple of GALs, no?
      Yes, you right, but i haven't programmer for GALs. Moreover, PAL/GAL programmer circuits too difficult to replicate at home.. CPLD like Altera EM7064 is a good choice, but i want keep a "retro" style, so DIP-packages more preferred...


        Most PROM programmers will also do common SPLDs like 22v10s and 16v8s. Also allows you to stick with 5V PTH target.
        "Good engineers keep thick authoritative books on their shelf. Not for their own reference, but to throw at people who ask stupid questions; hoping a small fragment of knowledge will osmotically transfer with each cranial impact." - Me


          - No need to decode A10 and A11 for I/O ports, most ISA cards don't...
          - Probably no need to decode A0 either... Does it matter if both 0x224 and 0x225 will read as 0x7F?
          - I'd try to avoid 74154 because it is slow and large. If possible use 74LS138 instead
          - ~IOCS16 is not present on 8-bit part of ISA, and yes, I/O card needs to decode AEN signal (or bad things will happen with DMA).
          - It might be possible to save U3 and all the related decode logic. Just put pull-ups/pull downs right on the internal data bus. TTL logic has relatively high "LOW" level input current (0.4-1.6mA depending on logic family). So the pull down resistor should be 1k or even less (470 ohm?!). The pull-ups can be 4.7K, or even 10K...


            Originally posted by eeguru View Post
            Most PROM programmers will also do common SPLDs like 22v10s and 16v8s. Also allows you to stick with 5V PTH target.
            Be careful there--I've seen some Chinese programmers that list the 22V10 as one of the devices, but it turns out that they can handle only the 20-pin GALs, such as the 16V8. That's one of the reasons I sold one that I had just purchased.
            Reach me: vcfblackhole _at_ protonmail dot com.


              Thanks for pointing out the error, my blog entry has been updated.
              My Retro Computing and Vintage Gaming Blog :


                Could be something like this:
                Game Blaster Address Decode.jpg

                The 74LS245 transceiver is enabled by addresses in 0x220-0x23F range (generated by the bottom 74LS138 ).
                The lower bits of address (A5..A1) are decoded by the top 74LS138. It generates chip selects for SAA-1099 chips and read/write enable signals for the 74LS374 flip-flop (I think 74LS574 FF, or 74LS373 and 74LS573 latches can be used instead).
                The pull-up and pull-down resistors drive the internal data bus (DB0..DB7) so the default value is 0x7F (that if nothing else drives it).


                  Thank you, but if it is possible put a bigger picture? I expect the arrival SAA1099 chips from China, during this time I can try to make autodetect...


                    Originally posted by Tronix View Post
                    Thank you, but if it is possible put a bigger picture? I expect the arrival SAA1099 chips from China, during this time I can try to make autodetect...
                    Sorry about the image size... for some reason the forum software insists on converting PNG image to JPEG. Attaching a ZIP file with the orignal image. If you really want I can send you KiCad schematic as well...
                    Attached Files


                      BTW, wouldn't it be simpler to hack a game and remove the detection code (and set it to a default value of 0x220, or use an environment variable)? It seems that the described detection method only works with the Game Blaster, but not with SB 1.5 / SB 2.0. So hacking the game will make it usable on these cards as well.


                        Today i get some time to build CMS replica... I used mostly Sergey's circuit for auto-detect part except 10k pull-ups. If i read any empty port i get 0xFF value, so i think motherboard have internal pull-ups for data lines. Soldered auto-detect part from Sergey's circuit:

                        Did the test stand based on 386 CPU and install my device onto left ISA-slot:

                        And run TESTCARD.EXE from CMS diskette. So, this software successfuly found CMS:

                        Then i soldered two SAA1099 and 74HC74 for divide 14,3MHz by two. Audio outputs has not filtered, no amplifier. Just 1k pull-ups for all four output channel and then mixed by 10k resistive divider into left and right. Then output to headphones over 0,1mF:

                        It's worked! noisy, but work! I think needs to be done with the use of filter capacitors.

                        I recorded sound from this card:


                          Sounds very promising, and I would think that if it replicates DOSBox's CMS detection methods, then it would work with every game that requires the Game Blaster autodetection to work.
                          All you Russians, first the Adlib, then the SSI-2001 and now the Game Blaster! Perhaps the Covox Sound Master will be next. Will no 8-bit sound card be kept exclusive and ludicrously expensive?
                          Last edited by Great Hierophant; May 24, 2015, 09:26 AM.
                          My Retro Computing and Vintage Gaming Blog :


                            Originally posted by Tronix View Post
                            It's worked! noisy, but work!
                            Fantastic work, Tronix! Warms my heart to see the SAA1099 get some love.
                            Offering a bounty for:
                            - A working Sanyo MBC-775 or Logabax 1600
                            - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)


                              Nice work!

                              Audio quality: Adlib and SoundBlaster use active filters. Also the audio part is separated from digital, shielded (at least has a solid ground plane).

                              Not sure if reading an unused I/O address will always give 0xFF. Older computers (e.g. PC/XT) normally don't have pull-ups on data bus. And 0xFF might be a side effect of TTL inputs reading '1' when connected to Hi-Z state outputs. So I recommend put these pull-up resistors.

                              It is interesting to see some soviet/Russian chips on your board.
                              BTW, K155TM2 is an old plain TTL 7474; K555 series are 74LS analogs; K1533 are 74ALS.