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Thread: Tandy Sound Compatible PCB

  1. #31
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    Quote Originally Posted by pearce_jj View Post
    The full bill of materials with part codes for Mouser and Farnell will be published shortly
    That'd be cool. I'm going to build my card with a socket for the SN76489AN, so I can easily swap it for other models and experiment (I know at the very least that there are two types of noise generators).

  2. #32

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    What is the other chip you are thinking of?

    Wiki page is up: https://www.lo-tech.co.uk/wiki/Lo-te..._Sound_Adapter

  3. #33
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    Quote Originally Posted by pearce_jj View Post
    What is the other chip you are thinking of?
    Well, I was at least thinking of the SN76489AN and the SN76496(A)N.
    Another one I was thinking of is the NCR8496, which was used in Tandy 1000 machines: http://www.vgmpf.com/Wiki/index.php?title=NCR_8496
    But apparently they changed the order of the data lines on that one, so it won't be a plug-in replacement.

    The Sega's with different noise channel are apparently the integrated ones, so those are out as well, I guess.

  4. #34
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    The NCR8496 is a drop in replacement for the SN76496, as indicated on Technical Manual - Page 2 as shown in that link. Information about noise channel in various chips can be found here : http://www.smspower.org/Development/SN76489, but I am not persuaded that the implementation of the feedback bits would result in audible differences between the TI and NCR chips. But there is a difference in some music, compare the Maniac Mansion recordings here : http://nerdlypleasures.blogspot.com/...ound-chip.html
    My Retro Computing and Vintage Gaming Blog : http://nerdlypleasures.blogspot.com/

  5. #35
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    Quote Originally Posted by Great Hierophant View Post
    The NCR8496 is a drop in replacement for the SN76496, as indicated on Technical Manual - Page 2 as shown in that link.
    Okay, these chips really have way too much misinformation on the web...
    But yea, the NCR8496 is indeed pin-compatible if it is a drop-in replacement (which makes sense... why build a clone when you don't make it a drop-in replacement?)... and the SN76494/SN76496 manual specifically says they can be used as a replacement for the SN76489A: http://www.datasheetarchive.com/dl/5...7779/O/SN76496
    What that manual seems to say however is that the 94-variation has the divide-by-8 removed, so it needs a ~500kHz clock signal, where the 96-variation has the divide-by-8, so it takes a ~4 MHz signal, like the 89.
    So that means the 96 is the one you can use as a drop-in replacement, and the 94 you could use, but only if you add an external divide-by-8 circuit on the clock.
    The manual doesn't make it clear what the difference is between the 'A' and the regular version of these chips though.

    At any rate, I think my list of possible chips so far would be:
    SN76489AN
    SN76496(A)N (I have not seen any pictures of the 'A' version online. Might be rare)
    NCR8496

    There may be others that are interchangeable (like the 'A' and non-'A' versions, but no conclusive info yet on what it actually means. It could be that inverted signal that Wiki says, but why isn't that mentioned in the manual then?).
    Last edited by Scali; November 20th, 2016 at 11:03 PM.

  6. #36

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    Also re data bus numbering - the SN part numbers D0 as MSB for some reason.

  7. #37
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    I tried to apply some logic to the naming scheme...
    The SN764xx series basically uses the same old naming scheme as the 74xx series. So perhaps the same rules to the naming apply. SN would then indicate that it's a Texas Instruments chip. The 'N' as we already know, is the 'narrow' package. And the 'A' would indicate a higher 'electrical grade' version of some sort, it would seem:
    http://www.ti.com/lsds/ti/packaging/...onvention.page
    I think in this context that may mean a different (more robust) packaging material.

    Another theory is that 'A' is a revision... but I think that theory may only go for the SN76489 then. I only found a datasheet for the 'AN" version, but that implies that the regular SN76489(N) is different.
    Because the SN76496, and its A and N derivatives are all in the same datasheet. The datasheet does not mention any difference between the 'A' and regular versions, which makes me think it's probably just the packaging, nothing electric, so not different revisions of the circuit.
    In the case of the SN76489AN... it might be that the earlier version had the inverted output, and this was fixed in the 'A' version, but no non-'A' was produced anymore.
    Last edited by Scali; November 21st, 2016 at 01:44 PM.

  8. #38
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    Right, I've looked on Ebay, and I've found a few SN76489AN and SN76496N chips. No SN76496AN, nor any NCR8496.
    This should do for now

  9. #39
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    I've finally found some conclusive information regarding the 89N vs the 89AN:
    http://www.datasheetarchive.com/dl/2...51d/O/SN76489N

    So the A is indeed a different revision in this case, and its output circuitry is modified somewhat, the output can now only drive 10ma, instead of the 100ma for the non-'A'.

  10. #40
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    Is the difference in the power output level likely to change anything? I see that the -A version can driver a small passive 8 Ohm speaker and the A version cannot. I would think therefore that increasing the resistance on the potentiometer for the PSG sound on the board may be able to compensate for the higher volume level. The output current for a SN76496 is also 10mA according to its datasheet. The SN76496 datasheet also says that the audio pin should be grounded if not used, although IBM appeared to leave it floating in the PCjr.
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