Looks like a good price for a reasonable board - except for the 40 pin connectors. One only has two GNDs, the other has 10 but they are somewhat clumped together.
I question whether there might be (unnecessary) signal integrity issues with tightly specified high speed signals.
How's the quality of the BeScope?
Not bad at all for just $50, the thing I'm more exited about is the SDP Interposer so I can connect to other Analog Devices boards.
http://wiki.analog.com/resources/alliances/altera
Also the connector Analog Devices uses is a Hirose FX8-120S-SV that mates with the FX8-120P-SV in the Interposer, they are fairly cheap.
How's the quality of the BeScope?Pictures of the device generating 2.5MHz and 5.0MHz ringing square waves as well what the DS2202 sees.
For us to understand the significance of that ringing, you have to define the probe used and how it was connected to the board.
And then, when considering the lack of GND pins on the 40-way connectors, see what happens w.r.t. ground bounce when many outputs simultaneousl switch in the same direction.
As far the lack of GND pins I'm not sure what are you talking about, it has 2 GNDs one 3.3V and one 5V on the Terasic 40 pin connector.
The custom one has 10 GND pins out of the 40, and the 80 pin connector has 23 pins that I can't find assigned, I will have to look at the schematic if they are all connected to ground, pins [30-34] and [61-80]
For us to understand the significance of that ringing, you have to define the probe used and how it was connected to the board.The ringing is just be cause of the oscillator generating the 2.5MHz and 5.0MHz test signal.
I was just probing the in board test signal using both the ground and the signal pins on the test signal.
QuoteAnd then, when considering the lack of GND pins on the 40-way connectors, see what happens w.r.t. ground bounce when many outputs simultaneousl switch in the same direction.
As far the lack of GND pins I'm not sure what are you talking about, it has 2 GNDs one 3.3V and one 5V on the Terasic 40 pin connector.
The custom one has 10 GND pins out of the 40, and the 80 pin connector has 23 pins that I can't find assigned, I will have to look at the schematic if they are all connected to ground, pins [30-34] and [61-80]
Very unlikely, since the oscillation frequency is independent of the clock rate, probably around 100MHz.
I'll bet your probe has a 6" ground lead and croc clip, and a ~15pf tip capacitance.
And it's just a test signal. it reads my 1khz test signal from the scope without ringing.
Also probing without ground since the test signal ground is the same as the scope module produces the ringing, so I'm not worrying too much about it and it's kind of off topic. I was just saying that for $50 he can get the bundle instead of paying $49 for just the dev kit. The interposer alone goes for another $50 for example. And the BeScope by itself is $45, the probe is a cheapy $10 100MHz, so you are getting $150 worth of things for just $50
Very unlikely, since the oscillation frequency is independent of the clock rate, probably around 100MHz.
I'll bet your probe has a 6" ground lead and croc clip, and a ~15pf tip capacitance.
Yeah, this is probably the case. You can make a quick short ground probe using a piece of insulated wire. Start by taking the "witch's hat" off of the oscilloscope probe then strip both ends of the insulated wire and wrap one end around the metal ground shield of the probe. Thicker gauge wire is a bit better because you can bend it and it will keep its shape. Pick a ground reference point close to where you are probing.
It takes some effort to master holding the probe tip and the ground probe in place with one hand. We have some real Tektronix short ground probes at work, but most of the other engineers tend to prefer the wire wound probes better. This will likely remove some of that edge oscillation if you keep the wire short.
I've driven that DAC up to 1600x1200 at 60Hz, so 162 MHz pixel clock. Edit (using that 40 pin connector)
In this capture it shows the time for 256 values. So multiply the 1 over delta X to get the approximate pixel clock.
I said the pins can be configured to do differential signals. Those are not the case in there.
Also my 200MHz scope with 300MHz probes at 2Gsps falls short even for the 330MHz measurement.
In any event, the BeScope measuring its own test signal with the ground clip removed showed the ringing even with a shared ground with the test signal.
The ground on the test signal is the same ground on the scope barrel, are you clamming that's not properly grounded if I use the probe with the ground clip removed?
(the signal is labelled as CLK Out).