Altera Cyclone II mini board: why hardwire external pins? - Page 1
Forum section: electronics / general

author: obiwanjacobi
author_rank: Super Contributor
timestamp: May 21, 2020, 08:49:11 am
content: I am lookingat the schematic of a cheap ebay Altera Cyclone II mini boardand I am wondering why they chose to short 4 pins (pins: 26, 27, 80 and 81) to 1.2V and GND - pins that also are exposed to the pin headers (P2 and P4)?Based on the pin documentation of the Cyclone II (T144)they are just normal IO pins (with a differential function)...I would understand if they would not be used - when there is not enough room on the pin headers to break them out, but that is clearly not the case.Why?At this point I am thinking of simply removing those zero Ohm resistors (R1, R2, R9 and R10) to get use out of those pins...

author: oPossum
author_rank: Super Contributor
timestamp: May 21, 2020, 09:10:13 am
content: That may have been done to support another part in the same package that does require power on those pins.

author: BrianHG
author_rank: Super Contributor
timestamp: May 21, 2020, 09:14:48 am
content: Quote from: oPossum on May 21, 2020, 09:10:13 amYes, the larger core of the EP2C16/EP2C25 requires more current for their larger core, hence those IOs are changed into VCCint & GNDint. I hope that board's regulator can handle it if you goto the larger FPGAs...

author: obiwanjacobi
author_rank: Super Contributor
timestamp: May 21, 2020, 09:16:02 am
content: Package as in the board or the Cyclone II chip?Edit: I see you mean the chip.There's practically nothing on the board.

author: obiwanjacobi
author_rank: Super Contributor
timestamp: May 21, 2020, 09:24:10 am
content: Quote from: BrianHG on May 21, 2020, 09:14:48 amOnly the EP2C5 and EP2C8 come in a T144 so is this a left over of a generic schematic ...?Seems to me I can safely remove these zero-Ohm R's.

author: BrianHG
author_rank: Super Contributor
timestamp: May 21, 2020, 10:29:16 am
content: Sorry, my mistake, I quoted the CycloneIII T144 devices.Yes, the CycloneII T144 EP2C8 has less IOs then the EP2C5 as listed in the CycloneII handbook on page 22.In the CycloneIIIs, this divide doesn't begin until it's larger devices which are also available in T144.https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/cyc2/cyc2_cii5v1.pdfIn my CycloneIII designs which use multiple generations like this, I usually just wire the VCCints and GNDints and make sure I keep those pins as inputs when compiling for a smaller Cyclone where those pins may be IOs.

author: obiwanjacobi
author_rank: Super Contributor
timestamp: May 22, 2020, 06:07:06 am
content: I think I need all the pins I can get on this one

author: james_s
author_rank: Super Contributor
timestamp: May 22, 2020, 06:14:36 am
content: I have about a dozen of these boards and I have always removed the zero ohm jumpers, also the resistor and capacitor that is wired to one of the other pins. I needed every pin I could get for my vector game. I've developed a bunch of projects for that board.https://github.com/james10952001

author: obiwanjacobi
author_rank: Super Contributor
timestamp: May 22, 2020, 06:23:18 am
content: I left the R/C to act as a reset pin... - but, yeah.I also hate it when they attach buttons to the pins without R's - an accident waiting to happen.Attached is a pin planner csv file (as .zip) you can import into Quartus I made to document this.

author: dentaku
author_rank: Frequent Contributor
timestamp: December 14, 2020, 02:00:23 am
content: I read about this problem and how it can cause the regulator to get hot on this Github page.https://github.com/linker3000/MulticomperI'm glad to see other people have decided to just remove the 0 ohm resistors and it works fine.I'm guessing the original purpose for this board needed these but when people started cloning them they just kept the resistors there for no reason.

author: james_s
author_rank: Super Contributor
timestamp: December 14, 2020, 06:18:39 am
content: They're required for the larger Cyclone II part in the same package, but I've never actually seen that part used on a board like this. I think whoever made these boards just blindly installed the entire BOM without questioning whether those jumpers were actually needed. I ran into this recently with low volume production product a friend of mine designed, the company they had build them installed a bunch of extra parts that weren't supposed to be there which resulted in a lot of extra troubleshooting time from me. They had populated a buck regulator but then also populated the jumper that completely bypasses the regulator and a bunch of other bits, it was obvious they never even looked at the circuit, just built it and ignored all of the "do not fit" notes.

author: dentaku
author_rank: Frequent Contributor
timestamp: December 14, 2020, 11:59:23 pm
content: Quote from: james_s on December 14, 2020, 06:18:39 amOK, that makes sense.I'm going to remove the jumpers on 26 and 81 then. I have this board but the programmer hasn't shown up yet so when I found out about those two pins being tied directly to 1.2V I wanted to make sure other people were OK with removing them.Like the original poster said, 27 and 80 are tied directly to GND so I might as well remove them too because the .PDF lists them as regular IO pins and I don't want to waste pins for nothing or risk shorting them.

author: james_s
author_rank: Super Contributor
timestamp: December 15, 2020, 03:45:43 am
content: I've been removing all of those jumpers on all of my boards, there's no reason not to. Initially when I released some of my projects I used some of those pins and forgot they had originally been tied to ground and vcc, caused problems for some people trying to replicate them.