On Sun, 10 Jan 1999 10:53:59 -0800 Gerhard Fiedler writes: >i don't understand the zener (if the supply itself is good). in a >latch-up >situation, the voltage after the current limiting resistor is likely >to >drop anyway, isn't it? The zener is to keep the Vdd voltage from going up because a spike has passed through a protection diode. Without the resistor, the low impedance of the system's power supply would do a fair amount to absorb such a spike. When the resistor is added, this inherent protection is lost. However, the resistor would help limit damage to the multiplexer and zener in case of a really big spike. ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]