Steve's DFB1 build

[Steve]

It's ok thats just a bunch of 0805 4k7's, no issue.

@Badwolf By the way C1, is that a 10uf?

[Badwolf]

It's ok thats just a bunch of 0805 4k7's, no issue.

That was a wind up. 0805s and 2012s are the same thing. ;)

@Badwolf By the way C1, is that a 10uf?

Yep, there are a few 10uFs about the place. I've got C1 as 10u and C2 as 100n, but depending on your weapon on choice on the regulator front, the data sheet might recommend them the other way around.

I tend to wing it when I put them together. I suspect some of my boards they're one way around and others the other. It's not been scientifically calculated based on trace length or anything like that. :)

BW

[Steve]

Cheers :)

[sety]

Who do we think the best is actually, guys?

Element 14 has been really good lately. Only took them a few days to get the cpld to me.

[Steve]

Just an update to the build:

Basically just need to add the TT ram & then program the CPLD. 3v3 regulator and a few passives.

PXL_20220409_195351555.MP.jpg

PXL_20220409_195341120.MP.jpg

[Badwolf]

Looking good, @Steve

It should work fine without the AltRAM and I'd recommend you try it like that first, to be honest. Makes a possible bughunt later easier.

I'm not convinced socketing the FPU oscilaltor will let the keyboard close -- let me know how you get on with that.

Be very careful with the regulator. If you're not 100% confident you've got the right one (pinouts!) then I'd power the 5V rail from a bench supply (limit at about 150mA) and see if you can flash the CPLD in vitro.

BW

[Steve]

Hey @Badwolf

Prob a silly question but I assume I can test power the board with the 5v & GND points here under the Xtal? By the way I tested continuity across them and found there isn't one single 5v point here, the top three are all 5v and the bottom three are all GND, not what the silk screen suggests?

PXL_20220414_183506597.jpg

[Badwolf]

Hey @Badwolf

Prob a silly question but I assume I can test power the board with the 5v & GND points here under the Xtal? By the way I tested continuity across them and found there isn't one single 5v point here, the top three are all 5v and the bottom three are all GND, not what the silk screen suggests?


PXL_20220414_183506597.jpg

Hi Steve,

Yep. Sorry if the board isn't clear: three 5V pins, 3 GND pins (for tapping power to external items).

There's a 3V3 version on the other side (only 2x2 that one).

BW

[Steve]

Hey @Badwolf

Prob a silly question but I assume I can test power the board with the 5v & GND points here under the Xtal? By the way I tested continuity across them and found there isn't one single 5v point here, the top three are all 5v and the bottom three are all GND, not what the silk screen suggests?

Hi Steve,

Yep. Sorry if the board isn't clear: three 5V pins, 3 GND pins (for tapping power to external items).

There's a 3V3 version on the other side (only 2x2 that one).

BW

Sorry - just trying to be crystal clear here, you say 'for tapping power to external items', but this also can be used to power the board? (It is just the most convenient place for me to do so)

ps - I did put 5v to the board and my LED's didn't glow like yours, the chip also didn't get hot. Perhaps it's to do with current, my bench psu has current/amps but I do get confused with how in the video you're worried about how much current to allow, surely the chip only pulls what it needs when it comes to current? Or is it because you're worried about a short, which would make a lot of smoke if the amps were too high? (I guess this is correct)

Tonight I'll have my Pi Xilinx programmer working, do I need to provide 5v to the board for the programming or will the Xilinx cable provide all the power required? I think it says 3v3 and gnd on the cable.

PXL_20220415_100552890.jpg

[Badwolf]

Sorry - just trying to be crystal clear here, you say 'for tapping power to external items', but this also can be used to power the board? (It is just the most convenient place for me to do so)

Yes, the 5V rail is contiguous throughout. You may power the board from there.

I used a VCC pin on the FPU socket, for example. They're all direct shorts to the VCC plane.

ps - I did put 5v to the board and my LED's didn't glow like yours, the chip also didn't get hot. Perhaps it's to do with current, my bench psu has current/amps but I do get confused with how in the video you're worried about how much current to allow, surely the chip only pulls what it needs when it comes to current? Or is it because you're worried about a short, which would make a lot of smoke if the amps were too high? (I guess this is correct)

Yes, worried about a short, worried about a design flaw (was first time that revision was powered up), worried about a failed part etc.

Whether the LEDs come or not depends on the initial pre-programmed state of the part, so will be random. I think I had some on even after doing an erase.

Tonight I'll have my Pi Xilinx programmer working, do I need to provide 5v to the board for the programming or will the Xilinx cable provide all the power required? I think it says 3v3 and gnd on the cable.

No the programmer does not power the chip. I think I mention that. The 3V3 line on the programmer is a sense line. When it detects 3V3 its LED goes green.

BW