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kgallen

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Everything posted by kgallen

  1. kgallen
    -My apologies, on which schematic is this Q5 transistor you speak of.- <Hey, where has "strikethrough" gone when doing Edit???> Ah, on the 640 schematic, I was on 770 where it's Q34. This can be used in I2C for flow control - the slave holds SCL low to tell the master to extend the I2C cycle (I2C spec $3.1.9). But also you are right, this can also be used in multi-master I2C topologies as a means of bus arbitration (I2C spec $3.1.7). My second apologies, I am still commenting and disturbing your peace despite my assertions to the contrary :-(
  2. kgallen
    I believe I made (at least!) one incorrect assumption or statement earlier in my voyage of discovery. In reviewing/perusing my pdf attached above for 770, I realise that for a keyboard, the deck is an I2C slave (SCL is input to the deck, albeit with flow control from the deck using transistor Q34[770]/Q5[640], SDA seems input to the deck only). For PC-Link the deck is I2C master (or indeed could be master or slave) (SCL is output or bidirectional, SDA is bidirectional). This means that to support PC-Link, the "keyboard pcb" cannot have any active circuitry that would prohibit driving out either SDA or SCL. Active circuitry could of course allow this, but if the deck was intended keyboard-only then the active circuitry may be unidirectional as detailed above.
  3. kgallen
    @NGYAre you able to share (without major document preparation on your behalf!) the next step that I feel you know the answer to? I realise you want to fully validate your findings but of course this may depend on having a suitable deck and "vandalising" one's main machine is never to be taken lightly, so there could be a significant timeframe involved here. You are teasing us with the answer ;-) Is there anything next you need help with to bring this to a conclusion in our minds? I cannot help with the soldering iron, since the lead on mine will not reach to your workshop :-D Maybe you just want some space in your mind for this, without the chatter in this thread, in which case I abate!
  4. kgallen
    But on starting this, I did not know you were doing this so embarked on my own investigations per the initial request from @sfbp. I realise you want to present the perfect solution, but even if you share some thoughts then we can collectively learn and collaborate on the way. My reading of your comments was you still had issues to solve. If you want to present the ultimate solution and have all of the answers but are not ready to share, then that "heads up" to us is useful. i.e. I can butt out if this is all old news and there is a known solution yet to be shared. That said, I don't think I've wasted my own time since I've learned more about an aspect of these machines I hadn't investigated before. However if I'm presenting old news at the frustration of others then I can stop. Above reads bitter, it is not meant to! Greatest respect to you all here, you are great friends if such can be stated given this is an open forum.
  5. kgallen
    OK you clever people here is my latest cut-and-shut based on the insight from @M1JWR and @BearBoy Per @NGY's comments, the PC-Link (raw I2C) is not buffered in the 770 (despite the block diagram suggesting it is, below). The key here is that if the unit has a keyboard interface, then the I2C (IIC DATA, IIC CLK) also needs to be available raw on the DIN connector. The Keyboard interface has this 5-transistor circuit between the uC and the DIN. Also the PC-Link has these two extra connections IIC BUSY and IIC POWER. I believe that @sfbp has all these connections in place on his 640, however I need to review the details (but need to pop off for now for a work meeting, so be back later...) Sorry this is a pdf - exporting as png/jpg/gif didn't have the resolution (however I'll also upload a png just so you can see what's in the pdf, so you don't get too excited...) Keyboard_PCLink.pdf
  6. kgallen
    Well there you go, you've been there, done that! No point in me interfering here any more, you've done it! Hardware is fixed. That's me done. Firmware then. Over to you :-P
  7. kgallen
    On the 640 it's next to the rear panel Control-A1(II) connector. This picture is flipped. For you with the lid off, looking from the rear and down it will be to the right just above the rear panel just down from the power supply section (big black capacitors)/just across from the S-shaped heatsink.
  8. kgallen
    Zero-ohm link. Commonly used to option in and out circuit elements within a product range. See them all over the place. Could be a wire link but more usually these (and those) days a chip "resistor", 0R.
  9. kgallen
    Sorry for the cut-and-shut picture: I wonder if you chaps have a 4-pin or 6-pin connector for CN820 on your 640 main board. Then if R826 and R822 are fitted on your KB board (probably). If so, then I think you could rightly label your KB connector as "Keyboard (PC-Link)" with no changes...
  10. kgallen
    I2C spec - used to be quite hard to come by, but easily found on't web these days here. There are three traditional modes, standard-mode @100kbps, fast-mode @400kpbs and Hs-mode @3.4Mbps (not really ever termed baud on I2C).
  11. kgallen
    Sorry, my bad. Here I go again... :-(
  12. kgallen
    Well I guess we could argue details, but I2C is "Inter-IC" so not really designed/intended for off-board driving over a traditional cable - you'd use a spec like RS232 and it's brethren for that.
  13. kgallen
    It probably would work but not be robust. The uC I2C ports are not designed to drive a cable. Having a read of the datasheet for that I2C buffer gives the background of why that chip is required in such I2C topologies wrt capacitive load and current drive etc. If the USB interface inside the MN10 thing were mounted inside the 640 and wired directly in, I suspect the buffer chip would not be necessary.
  14. kgallen
    Which is a crazy case in point. Several of us were most impressed by this piece of work - and one of the first truly inspirational posts I found when I joined this forum. And we would still like more details! Myself, I got as far as breadboarding the photodiode and transimpedance amp circuit, but got overwhelmed by the mechanical challenge of getting it inside an MD case - something you had achieved with grace. I have the Sanwa LP-1. And whilst this is a small device, using it on my 440 is still a clumsy affair, getting the head near to the OP. I would still be wary using this with my other "more valuable" machines. So your own solution is still a desirable project.... We can but ask nicely and hope you overcome your shyness :-)
  15. kgallen
    I truly understand not wanting to open a prized machine - I still hold that for my 520 which is in truth nothing special in this world, but held dear to me for no tangible reason other than sentiment. However @NGY it sounds that, much to your emoted chagrin earlier, you are in the ideal place to acquire such an experimental beast since your eBay world seems to be much more tempered than our own!
  16. kgallen
    There is collective nous here that I like to share my ramblings, since one of you fine chaps will either spot the error of my ways, bring some extra wisdom, or promote a new idea by the mechanism of "cardboard engineer" - that of just writing down one's own thoughts bringing clarity or a new insight into a problem. And long may it continue, fellow MD-ers!
  17. kgallen
    Hardware wise I would expect the 640 MB populated with the I2C buffer associated SMD resistors and DIN socket would be the hardware solution, because I2C can work like this (maybe also need to check for a single pullup resistor on each of SCL and SDA). The uC and firmware support is a harder question to answer and possibly only answerable by "just trying it" and the 640 seems the only viable candidate. My 440 is open to experimentation but it is at least two steps away from where we want to get to since it has neither KB nor PC-Link interface. If we did come up with an answer, I'm not sure Stephen's 50W plumbing iron is up to reflowing 0803 SMD resistors or TSOP ICs :-P How can I help answer your "last remaining step"? (The link took me to an earlier post in our conversation).
  18. kgallen
    Is there a machine with KB and PC-Link? I'd like to look at the schematic...
  19. kgallen
    Great news! I still don't understand the cause of the issue as first reported (recording issues with AA cell). Maybe I should have asked what a "Duracell AA8" battery is though. I know what a "Duracell AA" is!
  20. kgallen
    Related from the MDS-PC3 SM, captured for future reference...
  21. kgallen
    I think one of the comments to the video sums it up nicely: "Two minutes in, I desperately wanted one. Four minutes in, I didn't want one anymore."...
  22. kgallen
    LMAO! Looking at the schematics I would summarise as: - the JE640 keyboard interface is input only for the data. The buffer stage they've implemented here works keyboard -> uC only for data (the clock, SCL, is bidirectional since it's driven out to the keyboard but in the I2C protocol the slave (the keyboard) can hold the clock low as a flow control mechanism). - the S50 PC-Link interface is pure birectional I2C. I suspect the deck uC is the bus master but data can flow in either direction. The implementation uses a specific I2C buffer chip (listed above) to buffer the I2C bus from the uC to be able to drive out on a "long" cable to the slave device (this MN10 thing that is mentioned). So it's perfectly possible that on the JP model, they've hung both of these buffer circuits from the uC-side I2C bus (since I2C is specifically designed to work like that). Indeed if I look more closely at the S50 vs 640 schematics, maybe if both sets of components are populated on the PCB, then given the firmware support within the uC this support may indeed be possible on the 640 (subject to uC equivalence flagged by @NGY earlier). Indeed looking more closely at the 640 schematic, the discrete buffer stage is between the true I2C bus, which does appear on the KB connector *on the main PCB not necessarily on the deck connector* and a separate set of "KB" I/O on the uC. It looks like the PC-Link also uses this (non-standard I2C) "IIC-BUSY" signal which is not brought out on the 640 KB interface. More investigation needed, leave it with me...
  23. kgallen
    Yea... @Richard is suggesting he's bad with Forum software but he's got nothing on my incompetence with software in general (or more specifically Operating Systems and "Apps" as we seem to call everything these days). Computers are a work tool for me but 'cos I use them all day long people (inc family) think I'm "in IT" and can fix any computer malady they can throw at me! < string of emoticon's required here! > (In a Tarzan guise) "Me Hardware, You Software" :-D
  24. kgallen
    Thanks! I will persevere with this Unread option a little more. At this point I don't have any "unread" in MD->Tech so I will need to try this when there is some new content. Good shout though, thanks!
  25. kgallen
    Absolutely not! Your diligence is impressive and greatly appreciated - nothing worse than reading a thread and all the links/images broken. I didn't intend to knock this work in the slightest, more as a means to illustrate the issue I've seen. This usage issue I see both with this new "shiny" forum installed Mar/Apr 21 and with the previous version. Also Emoji's would be good! (Stephen is now groaning...!) Carry on McDuff, sterling work!
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