Are 7438s in DEC interfaces special?

Ethan asks: I'm not sure about Emulex, but DEC qualified all their Omnibus/Unibus/Qbus drivers and receivers for leakage current lower than the manufacturer's specifications, and for better Vol specifications at high current. This is necessary if you have a long bus, such as two Omnibus boxes with two backplanes each, etc. If you don't have a lot of loading on the bus, it's not too critical. To measure leakage current, make sure the output of the 7438 is NOT being driven (for instance, by setting both inputs low), then connect a microammeter between the 7438 output and +5V. Don't do this with the 7438 actively driving the output low, as you could damage the meter. For Vol measurement, you just need to set up a 70 mA regulsted current source from +5V to the 7438 output, and set both inputs of the 7438 high so that the output is driven low. Then measure the output voltage. A fancy circuit to do this, allowing you to dynamically control the current, may be seen in a Maxim appnote: http://www.maxim-ic.com/appnotes.cfm/appnote_number/177 However, for just a fixed 70 mA current, you can use just a linear regulator with a resistor, as shown on page 4 of National Semiconductor application note AN-103: http://www.national.com/apnotes/PositiveVoltage-Fixed__v3.html Note that the leakage current is a concern on both bus drivers and bus receivers (or transceivers). Also note that the leakage current and Vol vary with temperature and supply voltage, so if you really want to do this right you need to test at the limits. I suspect that the worst-case corner is high temp and max voltage, but I don't know that for a fact. I haven't actually tried doing any of this, so take it with a grain of salt.