>>----------
>>From:  jim ruxton[SMTP:cinetron@PASSPORT.CA]
>>Sent:  Monday, February 24, 1997 6:26 PM
>>To:    PICLIST@MITVMA.MIT.EDU
>>
>>I am designing a small digital voltmeter and current meter to build into a
>>piece of equipment. I'm probably going to use a 16c73 or 16c74.
>>  I would like to be able to measure 0 to 40 Volts and 0 to 20 Amps. In the
>>lower range ( 0 to 25 Volts) I wanted .1 volt of resolution. If I feed the
>>input voltage through a 5.1:1 voltage divider network and  into an A/D pin
>>clamping the voltage at 5 volts I should get .1 volts per step ie. 255 =
>>25.5 volts, using Vdd = 5 volts as the reference.  [ ... ]

If you are going to use 16C74 you should keep the reference voltage
 3.0V < Vref < 0.70 Vdd according to Errata sheet 74_e3a3, which can be
found on the Microchip website. There is a newer errata sheet too, 74a_b1e1,
that don't mention this problem so maybe they fixed it.  Anyway, just be
aware that you might have a problem if Vref is too high.  It's easily fixed,
just scale your input voltage accordingly.

Regards
Michael