From: not@telling.you.invalid   
      
   Hello,   
      
   I am working on a circuit in which I want to use 74164 SIPO   
   Shift Registers as something like basic DACs (Shift Registers   
   outputting a stepped current).   
      
   Whatever you want to call it, it involves connecting the   
   outputs of the 74164s together through individual high value   
   resistors so that current increases with each output going   
   high, the parallel output driving the base of a transistor. I   
   couldn't see a problem with the idea until I read this line in   
   "Newnes Digital Logic IC Pocket Book" (P. 44):   
      
   "Note that normal totem-pole outputs should not (except in a   
   few special cases) be connected in parallel."   
      
   Nothing is said regarding what these "special cases" might be,   
   although if viewed from the perspecive of logic interfacing, I   
   can see how mine may be one of them. Indeed it seems likely   
   that the statement refers to cases such as in a wired-OR   
   circuit where outputs are connected directly, without series   
   resistors.   
      
   Nevertheless, I saw need for clarification so I searched books   
   and the internet for reference to TTL totem-pole outputs in   
   parallel, but found nothing to directly address my concern.   
   Hence I ask here for clarification on the matter.   
      
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