Hi guys,
   Any chance of a quick sanity-check?

   I'm playing around with a design that needs to drive a bunch of 
open-collector outputs to a 5V-powered peripheral, and receive data 
along a bunch of 0V/5V open-collector lines back from said peripheral.

   The drivers specified in the datasheet for the device are the 7438 
"or similar" (so 7407/74LS07 would work too) for the O/C drivers, and 
74LS14 plus a 1k pull-up to +5V for the receivers.

   The thing is, the rest of my hardware operates at a Vcc of 3.3V, not 
5V. I was originally going to use some level translators to convert the 
3.3V to 5V then use LS07/LS14 chips to drive the I/Os, but then I found 
out about the TI 74LVC series:

74LVC07A: http://focus.ti.com/docs/prod/folders/print/sn74lvc07a.html
74LVC14A: http://focus.ti.com/docs/prod/folders/print/sn74lvc14a.html

   The datasheet for these specifies a Vcc of 0V to 3.6V (for the LVC14) 
and 0V to 5V for the LVC07. Input voltage is specified as 0V to 5.5V 
regardless of Vcc voltage -- even the LVC14 can apparently take a 5V 
input, despite its Vcc being limited to 3.3V or less.

   Somehow this doesn't seem right -- these are CMOS parts (LVC = Low 
Voltage CMOS), so surely there are parasitic diodes to Vcc and Vss, 
which would prevent any input from being driven above Vcc without the 
chip latching up?

   Am I missing some critical point here?

Thanks,
-- 
Phil.
piclist@philpem.me.uk
http://www.philpem.me.uk/
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