standard I/O cells. Need for I/O as standard cells

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senmerida

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What is a standard cell (I/O), and what is the need of I/O as a standard cell?
(its about I/O cell. Not an I/O port)
 

I hope you already know what is "the standard cells library". If not in two words: the standard cell library is a set of difference type of general purpose gates,flip-flops etc. for example NOR, NAND, XOR, INV. Also possible 3 input NAND, NOR etc, library could include 2X, 3X... NAND or NOR gates, where 2X mean gate can pass 2 time bigger current. They are not specially designed gates. they have same logically function NAND, 2X NAND, or 3 input NAND, all of them are NANDs.
the Same picture in I/O standard cells. There are a set of I/O: I/O cells for 1.8V, I/O cells for 2.5V, I/O cells for 3.3V, with 2mA output currents, with 4mA, 6mA. Logically there are the same, difference only AC/DC characteristics.
 
Thanks for the answer.
But why are we exactly using a normal I/O cell as a standard I/O cell. What is the need for that standardization of I/O cells?
 

most of IC-to-IC, IC-to-apparature interfaces are standartized (see PCI, TTL, CML,... standards in JEDEC documents). They define electrical and logical requirements to physical parts (i.e. I/O) of the interfaces,- like input/output switching levels, loading conditions,... That is why there are standards 1.8V CMOS, or 3.3V PCI,... I/Os. Everybody user will know, that TTL I/O shall provide minimum necessary number of definite electrical recuirements.
 
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