Another Modem and a Canon XT Clone

I’ve come back to my parents to visit them again and have found some more interesting hardware hiding away including two modems and an old PC clone belonging to my younger brother. Unfortunately for my Dad, internet providers aren’t very good at providing good service to rural areas, he is too far to get any kind of ADSL service. This had meant that for much longer than others he had to rely on dial-up until alternatives became available.

I forgot to bring my own camera, but was able to borrow my mothers, which whilst it has a higher pixel count it didn’t seem to do as well in the shots I took. I’ve had to adjust these images for brightness particularly.


This Dynalink modem is a pretty basic USB modem, I unfortunately couldn’t open it for any internal shots but it’s probably not very interesting as it’s small and almost certainly a software modem of some type. Dad used it for some time and had problems with drop-outs so we went about getting a better modem.


So we got this modem, a SmartSwan Turbo which much like my own modem is a proper self-contained serial modem you can use without drivers. This one was bought a little later (sometime around 2003 I don’t really remember) and did perform quite a bit better than the Dynalink modem. Unfortunately given the line quality and distance to the exchange there were still some issues, mostly speed and the very occasional drop-out.


I was able to take this modem apart quite easily, just four screws on the bottom. Here is an overview of the main board, you’ll notice that it is an Ambient chipset and is a voice modem (although we didn’t use that feature). Unlike my modem this one does have a line transformer and a DIP mask ROM chip for the firmware. It also has some similar features, like what appears to be a rectifier chip in the modem front end. Interestingly there is a 74 series logic chip (surface mount) towards the lower right of the board, something that has become unusual in modern equipment.


Here are the two primary chips up close, I believe the left one is the main DSP doing most of the grunt work for the modem, the one on the right looks like the serial interface. I found it difficult to find the data sheets for these chips as Ambient was formerly Cirrus Logic and now is a part of Intel. The chips were made late in 2002 so Dad probably bought this about the same time I got my modem.


The front end has fewer protection devices and simpler circuitry with fewer passive components. It may be using an older design with some updates. Not being an analog circuit (or any kind of circuit) guru I can’t really tell. Next up I took some photos of an old XT PC clone, a Canon A-200 20HD. My younger brother bought this machine for basically nothing, which is extremely lucky considering how hard they are to find in working condition. I found an article on google books here that reviewed the machine when it first came out, you will need to scroll up to read the whole article.


The machine in all its glory! It is lucky enough to still have the Canon branded monitor and keyboard with it, everything seems to have yellowed quite badly, although at least it’s uniform. The keyboard is still nice to type on and doesn’t seem to have any defects, although it does have the older XT style layout. The keyboard is compatible with the IBM XT class machines so it is possible to use it on another machine or replace this one if needed. The monitor is a pretty basic green phosphor monochrome monitor that seems to have been treated quite well. There doesn’t seem to be any burn-in and it is still quite bright and easy to read.


Here I’ve pulled the lid off to expose the internals, you can see a Canon 360k 5.25 inch floppy drive and a 20Mb NEC hard disk that has unfortunately stopped spinning. Fortunately I have some MS-DOS 4.01 floppies that allowed me to boot the machine, but it took ages to get to the normal prompt. In the expansion slots you can see a memory expansion card, the graphic card and hard disk controller. The floppy, serial and a parallel controller are integrated on the main board which means there are some slots free for further expansion. The main processor is an 8086 at 4.77Mhz which can be at times significantly faster than the 8088 found in IBM PCs at the time. This is because the 8086 has a 16 bit data bus (as opposed to 8) and could move data and instructions faster over the bus.


Here is the graphics adapter, interestingly it is not a Canon part but is made by Twinhead judging by the logo on the board. I can’t tell if it is Hercules compatible but it most certainly is compatible with MDA cards. I didn’t get any clues from the chips as many are 74 series, memory or other generic chips.


This is a memory expansion card, these cards frequently have a few different devices on them as well. In this case what appears to be a real-time clock and a 25 pin RS-232 port. This card has 6 x 64Kb banks of extra memory (384Kb made with 4164 DRAM chips) which would have required a special driver for the machine to gain access to it. The machine finds 320Kb of ram, but this is most likely the memory on the motherboard.


Finally here is the hard disk controller, a Western Digital device much like a later 16 bit one I have in my spare parts box. This one is only 8 bit and has more parts on the board, one with an old school Toshiba logo. Controllers such as this one were very common in all kinds of PCs of the time. Unfortunately the hard disk doesn’t seem to work any more, perhaps it’s time this machine got an emulated hard disk of some type.

9 Responses to “Another Modem and a Canon XT Clone”

  1. 1 goughlui
    June 28, 2014 at 1:38 pm

    Lovely to see hardware as always. The Swann modem with the Ambient chipset is virtually identical to the insides of the later Swann Speed Demon. It’s almost as if they stuffed a different case on the outside and called it a new product. Ambient later was acquired by Intel, if memory serves me right, and they went on to make a decent run of PCI based 56k modems and then “disappeared”.

    The Canon XT is quite interesting – I’ve used the Canon 5.25″ drives. They have a unique “push button” style disk-lock, and press-again to unlock and it will pop the 5.25″ out a bit so you can take it out. Nothing this fancy on the Teacs and Panasonic/Matsushitas with the normal “rotate down” to lock type drives. It’s amazing I haven’t seen any Canon 5.25″ drives in yonks!

    Nice to see the Winchester MFM hard drive with the data and control ribbons … what a shame it’s not working anymore. The only one I ever used was a 40Mb Miniscribe, along with its iconic noises and “reliability” issues. Looks like that drive was a lucky one – the factory defect table looks blank!

    • June 28, 2014 at 11:41 pm

      Thanks for commenting 🙂

      That’s interesting about the modems, I wonder if they also had the same firmware or were different in terms of features enabled?

      I’ve had one of those Canon drives before, in fact it was the first floppy drive I used in our original PC, a Twinhead Superset 590. The mechanism worked great for years but eventually started to jam, and this drive is doing the same. Basically a bit of cleaning and lubricating got the other drive working smoothly so that will likely work on this one to. It’s interesting that out Twinhead PC had a Canon floppy drive and this Canon XT clone has a Twinhead graphic controller. Perhaps they were sharing parts or has a special agreement.

      The Winchester MFM drive used to work, but unfortunately doesn’t seem to spin up anymore. I wondered if a PSU issue might have caused this or if it’s a more sinister mechanical problem. I unfortunately didn’t have time to find out. I have a few other drives that may work in my spare parts box so that may be a solution, but I had heard about a modern 8 bit ISA card that allows you to connect IDE HDDs or compact flash cards to a older style PC such as the 5150 or XT class machines. It might be hard to find, but I’m sure it would be worth it.


      • 3 goughlui
        June 29, 2014 at 9:55 am

        Hmm. I’m not sure how it will work for XT’s, but I presume you were referring to the XT-IDE project. At least for the AT’s, the CF-part can be fairly simple. I treated my 486 to an IDE to CF adapter, with a suitably old-enough card that understands CHS mode.

        All I did was fudge up the CHS parameters based on x/16/63 where x was calculated to stay within the LBA limits of the card, or within the 1024/16/63 limit. Some industrial CF cards have datasheets with tables of CHS values too.

        So far, I found success with an Astone 256Mb card (they’re just rebadgers) and a Kingston 1Gb card (as a 1024/16/63) but curiously my A-Data 8Gb Speedy CF cards don’t work. After an Fdisk, they fail to return the same partition table after a reboot so I assume those cards only support LBA access mode.

        – Gough

      • 4 goughlui
        June 29, 2014 at 10:09 am

        Oh and about the drive not spinning up – as long as none of the motor driving transistors are actually fried, it’s probably the motor bearings getting stuck after sitting for a long time. Some rather intrepid people have done various things to bring it back to life, sometimes just temporarily – e.g. giving the motor a good tap (maybe upside down) or in some cases, even dropping the drive onto something hard.

        If you’re going to toss it, why not even open the top lid in a very “clean” room, use a screwdriver into one of the spindle screw points and gently try to coerce the spindle to move. If it moves freely, try powering it, and if it still doesn’t work then it’s probably something electrical. With any luck, given a clean enough room, the internal filters will take care of any “last bits of dust” and the drive might have a few more years.

        I’ve had to do this for a modern drive, due to a phenomenon known as stiction. The laptop drive had its heads *on* the disk, and because the heads and disk were both very smooth, they “welded” and the drive motor wasn’t strong enough to overcome this force, so manual intervention was required. All the data was recovered, however. That may have happened for this drive too, because even when it’s parked, it’s parked on the drive surface, unlike modern “no-touch” ramp-load/unload technology.

        As for the modems, I’m guessing that it’s probably the same, mainly because most modem chipsets were more specialized in the 56k era. If it wasn’t as expensive as a USR modem, then it’s likely to be less cusomizable. The USR modems were all based on TI DSP chips, so they managed to get upgraded from the 28.8k V.34 era to 33.6k V.34bis, then all the way up to 56k V.90. The modems were also able to run x2, flex and V.90 **in the same firmware requiring no reflash**. The earlier ones just didn’t have enough flash on the PCB to make it to V.92, but the later ones did.

        None of the modems I’ve met since can even match the USR modems credentials. It’s part of the reason they were so good at detecting voice, very useful for computer-based answering machine, fax, BBS and wardiallers. The Rockwells, on the other hand, I remember flashing between K56flex and V.90 depending on the ISP we wanted to use as some combinations of server + client modem worked better than others.

        None of the Rockwell hardware modems I know “grew” any modulations during their lifetime, and that’s likely because of the “hard wired” nature of many of the functions inside.

        I had really wanted to dump the EEPROM of a few of my modems for a peek in a hex editor, but I hadn’t got around to it because I was very busy, but it would be interesting just to see what’s in it.

        – Gough

        • June 29, 2014 at 7:23 pm

          Yes it was the XT-IDE project I was thinking of, which if I remember correctly is an IDE controller which has the ROM code required for an old machine to use it correctly. I have been meaning to buy some CF adapters and some cards as well as I would like something less likely to fail than a HDD, 256Mb would be plenty for my needs. Although so far the old IDE/SCSI drives have mostly been reliable. I didn’t plan on throwing the old drive out, partly because it’s my brothers rather than mine, and I might also be able to get it going as you suggested. I also need to remove the Nicad battery on that memory expansion board in case it leaks. But since I didn’t have time and I’ve already come home that will have to wait til next time I visit my folks.

          Thats interesting regard the US Robotics modems, I’ve never had any contact with them. Sounds like they had quite the flexible and powerful DSP chip in them. If they didn’t require new firmware to get those improvements, did they use drivers/software to enable those extra features on modems that could handle them? It would be interesting to find out which parts are implemented in software and which are in hardware on the various devices.

          I’ll have to get myself an ROM reader/burner, I did toy with the idea of implementing a reader/memory tester using an arduino. I haven’t had the time to do that yet.


          • 6 goughlui
            June 29, 2014 at 7:34 pm

            Sorry, I think I wasn’t clear – the USR modems did require firmware upgrades to get the additional modulations up from V.34, but the difference was it could run x2, V.90 and K56flex all within the same firmware. When V.92 came out, some could even firmware update to V.92 but the oldest 28.8k ones could not due to lack of Flash memory.

            Most of the other modems were only capable of one 56k modulation at a time – and mostly a choice between V.90 and K56flex because they were “Rockwell/Conexant” owners.

            All of this because they used a 92Mhz Texas Instruments DSP chip to do all the modulation and demodulation.

            Flash is nice, but flash has its own issues too – read disturbs, limited write cycles and limited retention times. I’ve had a few older Flash BIOS chips suddenly corrupt themselves due to age – they’re only guaranteed for 10-20 year data retention without being “rewritten”.

            – Gough

            • June 30, 2014 at 11:54 am

              Ah ok that makes more sense now! 92Mhz is a pretty powerful DSP, might have been better than some of the machines the modem were connected to!

              Compact Flash is probably quite good for anything DOS based, but not so good for windows machines. DOS and programs for it usually don’t write to disks very much in comparison, and with the aid of smartdrv not much reading would be necessary either. Partly because the data sets for most DOS stuff is comparatively small. It might be difficult to get compatible cards in the future as the media is gradually phased out. I have heard of devices for connecting SD Cards up to IDE interfaces, but I don’t know if they support CHS addressing.

              Flash gradually dying explains why some main boards with Flash ROMS stop working when they get old. I wonder how long mask ROMs and UV erasable EPROMs will last in comparison. Much older hardware uses them, and the UV erasable EPROMs might be adapted for use in place of some Flash ROMs with a bit of ingenuity. I’ll have to check my main board collection to see which ones should have their flash ROMS re-written and tested.


  2. 8 Miguel L. Martins
    March 19, 2015 at 2:59 pm

    Very interesting the Canon XT clone! It is good to have an old machine like that up and running!

    If the yellow color bothers you, you can dismantle the PC, prepare a mixture called Retr0brite and cover all plastic parts with it. Then, let them in the sun to get a good ultra-violet bath for a whole day and wash them at the end – they may become as white as they were on day one! Please, have a look at:


    • March 19, 2015 at 3:50 pm

      Thanks Miguel,

      I’ve considered doing it, not just for this machine, but a few others as well. Unfortunately the machine lives at my parents place and belongs to my younger brother, so I wouldn’t want to experiment on it too much. I have however revisited it and removed the barrel NiCad battery that threatened to leak. Photo’s here.

      I’m not usually bothered by yellowing as it’s the experience using the machine and playing with the hardware I enjoy the most. Although I do understand why people go to the effort to do it. Being strapped for time often limits how much tinkering I get to do, so I also usually try to do the more important things first.

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