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I have been trying to figure out the functional differences between TI's version of 74HC595 and NXP's version. I've been looking at the function tables in the datasheet for TI and the datasheet for NXP but am having a hard time determining if the function tables are equivalent. They have the exact same number of states and seem to be very similar. The confusion is arising from the fact that some values that are L or H in one table are X in the other table and that TI's version is missing the output columns.

If someone is able to figure out if these two chips are functionally equivalent, i.e., they do the same thing given the same input signals, I would appreciate some help. Thanks.

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When it comes to these sorts of logic ICs, if you match the part number you'll match functionality. So, a 74HC595 from NXP should 'work' the same way as a 74HC595 from TI. The pins are given different nomenclature by the manufacturers, but they do map 1:1 between the ICs.

If there were a functionality difference, then there would be a corresponding change to the part number:

  • Consider the difference between a 74HC595 and a 74F595 - both do the same logic function, but the underlying technology of the IC is difference (HC is high-speed CMOS, F usually refers to Fast which generally implies Schottky construction). There can be differences in timing and logic voltage levels as you change technology.

  • Consider the difference between a 74HC595 and a 74HC596: the 595 is what you're using (8-bit shift register with output latches, three-state parallel outputs) whereas a 596 is slightly different (8-bit shift register with output latches, open-collector parallel outputs).

Of course, even with the same number, there likely is very minor variations between them. The fundamental functionality and speed will be compatible and unless you're really pushing the limits of the IC, you should be able to substitute with confidence. (That being said, always test!)

The timing diagrams should clear things up:

enter image description here

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  • \$\begingroup\$ That makes sense. So if the function tables are different, does that imply that the functions are also manufacturer-specific and can vary? Also, is the timing diagram the most reliable source for checking how the chip 'works'? \$\endgroup\$ – Anshul Jan 16 '14 at 3:12
  • \$\begingroup\$ In general same number == same functionality, but the timing and electrical characteristics can vary a bit, but not much. But the way the functionality is documented can differ. \$\endgroup\$ – Wouter van Ooijen Jan 16 '14 at 7:49
  • \$\begingroup\$ In general, there won't be huge functionality differences between vendors if they have the same 74 series number so if you're not abusing the part or using it near its absolute limits, you should be able to substitute vendors with confidence. \$\endgroup\$ – Adam Lawrence Jan 16 '14 at 13:40
  • \$\begingroup\$ Just a note on this topic... I recently got an email from Digikey stating that the NXP 74HC595N, 112, has been changed to an "end of life" status. So don't use it in new designs. \$\endgroup\$ – Kurt E. Clothier Jan 13 '15 at 5:29

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