The IOB6120 is a multi-function expansion card for the SBC6120 that adds a number of enhancements. There are two revisions of this board, revisions A and B. The main difference in the revision B board is that a problem with the battery backup circuit to the SRAM memory has been fixed. Below are links to images and such for fixing revision A boards, along with ZIP files containing schematics, code, VHDL, etc.
A revision B board is distinguished by the addition of a diode array on the bottom side of the board. The revision A only has the 8 capacitors for the Xilinx.
I do not have a comprehensive list of cut here/add this type instructions for bringing a revision A board up to revision B. I should print the schematics between the two versions and go through them, at some point.
In February of 2012, Vincent Slyngstad emailed me to let me know there was a revision C board that had been done in 2009. Vincent took Jim's original B revision and did a spin on it, fixing the the battery back-up issue. His write-up on the revision C boards is located here.
- 74LS138 traces highlighted on layout
- Placement of diode on bottom side
- Placement of diode on top side
- FPGA L select line modification
- Flash L select line modification
- Status line modification
----- Original Message ----- From: "Paul Schmitt" <Paul.Schmitt@calix.com> Ethan, Here are my notes with Jim for the Diode fix. I don't know if Jim wrote up anything formal. Also enclosed are pics showing parts placement for each of the four select lines (black components are the diodes, blue are the resistors. I had access to some very nice lab equipment to work with SMT devices - unfortunately I myself am not that experienced in working under a microscope (as witness in the pics of the solder damaged stacking connector:-( ). The untiled.gif shows the etch you are interested in. I used low reverse current diodes available to me in our lab BAV70 70V 0.1A SOT-23 (two diodes with a common-cathode- hence the three pin package of which one lead is not used - Jim references single diode packaging in the enclosed email). I used 4K7 ohm resistors. I believe in most cases I cut a 'gap' in the etch of the select line and mounted the Diode across the cut, then found a VCC point somewhere alone the select line and removed the solder mask, bridging the resistor from the select line to VCC (or via a wire to VCC). VCC=0, 138 is powered by VCC_NV and non_NVRAM selects should be high. VCC | < > Resistor < ---+ | +---- 138|o----[<|----*----|non_NV device (powered off) When VCC = 0 and 138 select is high - no current should flow. When VCC is present, the connected device select should be held high, except when pulled down by the 138 output. Or same idea put a Diode (Cathode facing the 138 -|<-) w/a pull up to VCC - essentially making the ACT an open drain part on just the non NVRAM selects. ----- Original Message ----- From: Jim Kearney <email@example.com> Yeah, I saw that they were 0402 or 0603 size. I ordered some 5K1 in 0805, so I drew it with the bigger one. The 0805 package is just big enough that one could get solder to bridge between its end and the cap pad. All six of the assembled units work - half of them had minor issues, all of which were solved by fluxing and reflowing all the fine pins. As soon as I apply the ECO to them, I'll test the serial and parallel ports and send them out, and the kits too. All that's left is to finish the doc about the ECO and revise the builder's doc a little. ----- Original Message ----- From: "Paul Schmitt" <Paul.Schmitt@calix.com> Oh BTW - you noticed that the resistors I used was about 1/2 that size. So for FLASH_L it perfectly fit between the etch and the convenient thru-hole PAD. That was the easiest of the three due to this lucky break. Those resistors were so small, they would get lost in a solder blob, or the 30AWG wire would rip them loose. Paul -----Original Message----- From: Jim Kearney [mailto:firstname.lastname@example.org] The version of IE I'm using scales down large pictures automatically, so I forgot about that problem. Does this work with your web browser?: http://www.jkearney.com/SBC6120/ECO-A/ ----- Original Message ----- From: "Paul Schmitt" <Paul.Schmitt@calix.com> Hi Jim, Oh sorry - I now see your graphic on the top layer when I opened with Visio. It looks great. When I opened the drawing the first time, it was so large I had not noted the 'blow up' drawing to the right, and didn't understand what you meant by 'graphic' other than the board drawing. Visio opened the drawing with the correct sizing to one sheet - so I then saw the graphic. Anyway, I was thinking of adding the same annotation, but you've got it so you may as well go with it. Paul -----Original Message----- From: Jim Kearney [mailto:email@example.com] Okay, I saved a bottom image in the same place as 'bot-diode.jpg'. This time I set the colors to look a little more like the actual board. I should be getting the 2-pin diodes in the mail today. I plan to apply your fix to one of my boards and then I'll be able to compare the draw, effort, looks, etc., more directly. I think what I'll do with the kits is to document both, include the parts for the MOSFET fix (because I think it's easier with hand tools), and offer to send the diode parts if they want them. ----- Original Message ----- From: "Paul Schmitt" <Paul.Schmitt@calix.com> That looks great for the top side (3 of 4 parts of the fix). Can you provide the same of the bottom so I could also annotate FPGA_L. Thanks, Paul -----Original Message----- From: Jim Kearney [mailto:firstname.lastname@example.org] > Enclosed are pics of the diode ECO. I measured 8.3uA after the fix,11.65ma > prior to the fix. I'm curious as to what measurements you got? I'm not > sure how accurate my meter is, but anyway this fix looks good. Enclosed are I am measuring 4 uA, but this is using a meter that I don't trust and a resistor that I don't know the exact value of ;-) > some pics - note I'm disappointed that I hit the iron on the stacking > connector (one thing you learn with the microscope is that you have very > limited peripheral vision, and if the iron is not visible, it's usually That is easy enough to do even w/o a microscope... > Also, if you provide me two highlighted pics of: 1) FLASH_L etch by IC1, > IC10 and C8 and 2) FPGA_L etch on the back side of the board (between FPGA > IC12 and the SBC connector). I already have the pic you provided me with > highlighted etch relative to where I placed the diode/resistor of STATUS_L > and CF_L. I will be happy to annotate those drawings and write up the ECO > for you documentation. I tried drawing a graphic of your FLASH_L change yesterday - what do you think about this format?: http://www.jkearney.com/SBC6120/ECO-A/top-diode.jpg