why do they do this?

[mstechca]

I have been looking at IC's for my microcontroller programmer design, and what makes me disgusted the most is the fact that the pin organization of most IC's SUCKS.

Here's what I mean.

Lets take a 74HC688 8-BIT magnitude comparator for example. It seems that on one side, the data must be connected in an interleaved fashion. In order words, bit 0 of byte 1 to pin 1, bit 0 of byte 2 to pin 1, bit 1 of byte 1 to pin 3, and so on.

But whoever made the 74HC245 was smart, because each byte can enter the chip at its own end. One side has one byte, the other side has the other byte. This is the property I would like to see in every chip.

Interleaving the bytes just makes it more difficult to create the PCB on a single-sided board.

but why do they interleave the bytes?

 

[danielsmusic]

its probobly easyer to make to the chip otherwise i don't know.
i don't know why it would be easyer.
your not the only one who is angry at it, have you every seen the block diagram of a 4017 cmos chip.
i goes like 1 5 6 3 2 4 and so on.

 

[zachtheterrible]

Hey Mstecha, do you mean on the actual chip, the pins are weird? Or do you mean on schematics?

Because on schematics, the pins are always in diferent places because its just easier for whoever is drawing the schematic so they don't have to connect something on the other side of the chip. In a way its less complicated, but in another way, it only makes things worse when you're tyring to assemble the schematic.

 

[mstechca]

do you mean on the actual chip, the pins are weird? Or do you mean on schematics?

I'm talking about the chip itself.

 

[checkmate]

There are several reasons why the pinouts are as such, and external interfacing is only one of them. Maybe the chip is expected to be used on a double-sided pcb? For one, you would expect very much shorter length tracks if this were the case. Sometimes, it's just purely a case of easier IC layout.