"Jon Elson" <jmelson@artsci.wustl.edu> wrote in message news:447212D6.1060008@artsci.wustl.edu...> Have you verified where pin 1 is? I got tripped up a while ago with > Xilinx > using a center-of-side pin 1 on CPLD packages but a corner pin 1 on FPGAs. > Really dumb mistake, but pretty easy to do. > > JonI second this as a necessary check. The file I looked to for Xilinx CPLD orientation guidance (last time I specified orientation for a tech) had superfluous information. The text was shown along with a circle (or two). There was a specific cirle locating the pin 1 location that wasn't pointed out as *the* unique identifying feature and was not readily visible on the part without the right shadowing.
Building a board with Spartan 3 FPGA.
Started by ●May 22, 2006
Reply by ●May 22, 20062006-05-22
Reply by ●May 22, 20062006-05-22
No, they really are shorted, 1.2ohms. I will try verifying the pins again. Then soldering everything except the FPGA & Flash PROM to see what the state of the pins is. It would be very nice to compare to a really simple board/schematic however. Pavel
Reply by ●May 23, 20062006-05-23
"Telenochek" <interpasha@hotmail.com> wrote in message news:1148318946.683392.228470@j73g2000cwa.googlegroups.com...> > I am running into a problem: > Using my DMM, VCCAUX & VCCO seem to be shorted to GND. > At this point I am absolutely sure that they are shorted through the > Xilinx chip.It's probably nothing to worry about. Here are a couple of excerpts from a similar discussion on the SI mailing list: The reason is because of leakage current in transistors. As process technology progresses (180nm -> 130nm -> 90nm ...), the leakage current in a transistor gets bigger. That is, a transistor, even when it is "off", will have some current flowing through it. Also, you can pack more transistors onto a chip. Therefore, you end up with tens to hundreds of millions of leaky transistors, which leads to a low resistance when measured with an Ohm-meter. Because IC components are nonlinear, how much resistance you measure strongly depends on the ohmmeter's applied voltage. (Most ohmmeters don't apply a voltage, so don't expect a fixed value from your meter.) When measuring semiconductor junctions with an ohmmeter, the voltage developed (i.e., resistance) across a DUT will vary with the applied current, therefore, a different reading will be indicated depending on the scale (current source value) used. /Mikhail
