Of course... There is also the obvious.... Not to be used on any tri-stated devices! To me, this is any chip outputing on to a bus which has more than one chip's output tied to it. What happens is you chip goes to output disabled, then another chip plays with the lines, and the comparator indicates a false. I with the others, in that I trust the good reading and suspect a false as being incorrect. Many times, the false is due to loading or threshold voltages. IE the OE line reads fine on a probe, and the chip under test fails, the chip in the machine passes, but a scope shows a swing tom 0 to +3.3 volts, or something like that. The chip in the comparator works, caus it has no outputs to drive, but the chip on the board shows differently. In this case you have to examine the sources for the inputs, and the sinks for the outputs. Mike If you ever want to (un)subscribe yourself with TTL, you can send mail to: <Majordomo@flippers.com> with the following command in the body of your email message: (un)subscribe techtoolslist or from another email account, besides xxx@yyy.com: (un)subscribe techtoolslist xxx@yyy.com