• Re: Phase 0 ghosting/jitter - is this really normal?

    From Anthony Ortiz@21:1/5 to All on Tue Aug 30 12:50:09 2022
    Oh, FYI, I'm using the ReActiveMicro Universal PSU Kit UPGRADED IIgs Power Supply so it shouldn't be a PSU issue.

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  • From Anthony Ortiz@21:1/5 to All on Tue Aug 30 12:43:37 2022
    Hello world!

    I'm seeing an occasional error when reading from my peripheral board circuit, about once every 50 million reads, and I'm trying to narrow down the issue. I decided to pull out my card (from a IIgs) and put a blank one in and attach probes to just the
    ground and phase 0 (pin 40) and see a lot of ghosting/jitter or whatever that is and I wanted to see if you guys think this is normal because it doesn't look kosher to me!

    Probes at 1x: https://drive.google.com/file/d/1xaisSJ6kjPNAKoPKuPd1VkV0HrSmoYhj/view?usp=sharing

    Probes at 10x: https://drive.google.com/file/d/1pO1FS7R1Fo8lGp97Dbfhuf4htH0n2f1-/view?usp=sharing

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  • From Anthony Ortiz@21:1/5 to All on Tue Aug 30 13:49:49 2022
    I changed the mem depth from Auto to 24M @ 10x probe: https://drive.google.com/file/d/1jH3Sy9v4vxsuYMFACm742u1b5InfIEmJ/view?usp=sharing

    Phase1 seems worse: 24M @ 10x probe: https://drive.google.com/file/d/1J_hEXfwo-LB6IAbNVQPDBX1B8Z5QOWn1/view?usp=sharing

    I'm sure it's gotta be me, I'm no electronics expert, could definitely use some guidance. :)

    Anthony

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  • From Anthony Ortiz@21:1/5 to All on Tue Aug 30 14:21:51 2022
    Going through Sather's book again and I see I misunderstood the long cycle; I thought it applied to the 6502's internal phase 0/1 signals, but I was wrong, it applies to the external Phase 0 and Phase 1 signals (actually all 1mhz and 5mhz signals). So I'
    m guessing what I'm seeing is the result of this long cycle? I'm probably barking up the wrong tree here, lol

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  • From Kent Dickey@21:1/5 to anthonypaulo@gmail.com on Wed Aug 31 04:39:52 2022
    In article <5534e386-af45-4612-91cc-d55d3046c94cn@googlegroups.com>,
    Anthony Ortiz <anthonypaulo@gmail.com> wrote:
    Hello world!

    I'm seeing an occasional error when reading from my peripheral board
    circuit, about once every 50 million reads, and I'm trying to narrow
    down the issue. I decided to pull out my card (from a IIgs) and put a
    blank one in and attach probes to just the ground and phase 0 (pin 40)
    and see a lot of ghosting/jitter or whatever that is and I wanted to see
    if you guys think this is normal because it doesn't look kosher to me!

    Probes at 1x: >https://drive.google.com/file/d/1xaisSJ6kjPNAKoPKuPd1VkV0HrSmoYhj/view?usp=sharing

    Probes at 10x: >https://drive.google.com/file/d/1pO1FS7R1Fo8lGp97Dbfhuf4htH0n2f1-/view?usp=sharing

    I looked briefly at the 1x. You have a lot of ringing. First, some ringing
    is fine, if that's the way the circuit is designed. Old NMOS/CMOS stuff
    is not trying to balance driver and receiver impedence, so I would expect things to not look "perfect". If there is real ringing, it's only a problem
    if the amplitude is so much that it causes the receiver to misread the
    signal (so, a clock ringing so much that it could be intereted as a new
    edge is a problem). As I explain to many people--some ringing is usually
    fine, it needs to be severe to be a problem.

    But: you showed the image of your probe--that's very useful. And you're probing incorrectly. You need the tip of the probe to be within say 1cm
    of the signal to be probed. You can not attach a long wire, and then
    attach the probe to that wire. If you want to see a signal on the
    motherboard, the probe tip must go right down there. You can solder on
    a VERY SHORT stub of less than 1cm (I often solder on a resistor, and
    then clip the lead down to <1cm since I can easily hold a resistor with
    pliers, it's thinner than usual solid wire, and it makes the soldering
    easy. You clip off the resistance blob itself). Then attach the probe
    to that SMALL stub.

    It looks like in slot 2 you have a prototyping card with a breakout
    connector, and you've stuck some wires in the connector for the signal
    and ground. These wires look to be about 6 inches long, and you've
    attached the probe to these wires. If you put a resistor in that
    connector instead, clip it to be short (and get rid of the resistance
    part), and probe that. No soldering needed. Not as good, since you're
    using an effective 3cm stub (the connector counts against you, sorry).

    The best is to take a real card, like the card in slot 5, and find the
    back side of a through hole chip with the signal you want. Solder on a resistor lead, then snip it to be very short (5mm is very easy to do,
    3mm is great). Note: I don't use new solder usually, just melt the
    solder already there and it's enough to hold the stub. I find the probe
    won't really clip on to the through-hole leads as they are since there's
    not enough to grab onto beyond the solder ball. Then put the probe
    directly on that stub, and it should grab on easily. This is about the
    best I can do.

    One trick is to test out ringing by manually holding the probe tip on the signal as well, and see if the ringing gets better. If the 1cm stub shows ringing, try manually holding the probe and see if it gets better. If it
    still does, then there's just ringing on the signal. It happens.

    It's ok to probe "badly" if it's easy, or that it's not worth the
    trouble to probe properly. Try to look at the signals as "digital", and
    ignore kinks, ringing, etc.

    Kent

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  • From Anthony Ortiz@21:1/5 to All on Wed Aug 31 00:54:07 2022
    I looked briefly at the 1x. You have a lot of ringing. First, some ringing is fine, if that's the way the circuit is designed. Old NMOS/CMOS stuff
    is not trying to balance driver and receiver impedence, so I would expect things to not look "perfect". If there is real ringing, it's only a problem if the amplitude is so much that it causes the receiver to misread the signal (so, a clock ringing so much that it could be intereted as a new
    edge is a problem). As I explain to many people--some ringing is usually fine, it needs to be severe to be a problem.

    But: you showed the image of your probe--that's very useful. And you're probing incorrectly. You need the tip of the probe to be within say 1cm
    of the signal to be probed. You can not attach a long wire, and then
    attach the probe to that wire. If you want to see a signal on the motherboard, the probe tip must go right down there. You can solder on
    a VERY SHORT stub of less than 1cm (I often solder on a resistor, and
    then clip the lead down to <1cm since I can easily hold a resistor with pliers, it's thinner than usual solid wire, and it makes the soldering
    easy. You clip off the resistance blob itself). Then attach the probe
    to that SMALL stub.

    It looks like in slot 2 you have a prototyping card with a breakout connector, and you've stuck some wires in the connector for the signal
    and ground. These wires look to be about 6 inches long, and you've
    attached the probe to these wires. If you put a resistor in that
    connector instead, clip it to be short (and get rid of the resistance
    part), and probe that. No soldering needed. Not as good, since you're
    using an effective 3cm stub (the connector counts against you, sorry).

    The best is to take a real card, like the card in slot 5, and find the
    back side of a through hole chip with the signal you want. Solder on a resistor lead, then snip it to be very short (5mm is very easy to do,
    3mm is great). Note: I don't use new solder usually, just melt the
    solder already there and it's enough to hold the stub. I find the probe won't really clip on to the through-hole leads as they are since there's
    not enough to grab onto beyond the solder ball. Then put the probe
    directly on that stub, and it should grab on easily. This is about the
    best I can do.

    One trick is to test out ringing by manually holding the probe tip on the signal as well, and see if the ringing gets better. If the 1cm stub shows ringing, try manually holding the probe and see if it gets better. If it still does, then there's just ringing on the signal. It happens.

    It's ok to probe "badly" if it's easy, or that it's not worth the
    trouble to probe properly. Try to look at the signals as "digital", and ignore kinks, ringing, etc.

    Kent

    Hi Kent! Thank you so much for responding, this is a great explanation of what I've been doing wrong. I'll do what you suggested and see what it looks like. I figured the problem was likely to be me, and thanks to you I'll be able to make a more informed
    test from now on.

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  • From Kent Dickey@21:1/5 to anthonypaulo@gmail.com on Thu Sep 1 04:41:54 2022
    In article <25814600-6c5b-4bad-a427-5c437d501cafn@googlegroups.com>,
    Anthony Ortiz <anthonypaulo@gmail.com> wrote:
    I looked briefly at the 1x. You have a lot of ringing. First, some ringing >> is fine, if that's the way the circuit is designed. Old NMOS/CMOS stuff
    is not trying to balance driver and receiver impedence, so I would expect
    things to not look "perfect". If there is real ringing, it's only a problem >> if the amplitude is so much that it causes the receiver to misread the
    signal (so, a clock ringing so much that it could be intereted as a new
    edge is a problem). As I explain to many people--some ringing is usually
    fine, it needs to be severe to be a problem.

    [snip]

    It's ok to probe "badly" if it's easy, or that it's not worth the
    trouble to probe properly. Try to look at the signals as "digital", and
    ignore kinks, ringing, etc.

    Kent

    Hi Kent! Thank you so much for responding, this is a great explanation
    of what I've been doing wrong. I'll do what you suggested and see what
    it looks like. I figured the problem was likely to be me, and thanks to
    you I'll be able to make a more informed test from now on.

    I just wanted to reemphasize that the Apple II is very noisy, and I
    would expect most signals to not look all that great. There's a reason
    it's clocked at 1MHz. Ringing is generally not a problem at all on data signals as long as it's not happening near clock edges. And the clock
    will look bad since it's not really buffered and driven well--but it's
    OK since all the timing requirements take into account that it doesn't
    look good. The clock can ring, as long as the amplitude doesn't get
    close to crossing Vih/Vil thresholds as it rings. It's kind of surprising
    how bad signals can get before its a problem.

    Some circuits are designed to have bad looking signal integrity--especially
    if they are at relatively low speed. It's cheaper and works fine.
    Signals ring when the driver is too strong for the capacitance load, and
    TTL drives relatively strongly.

    Kent

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