Thursday, October 11, 2012

IC chip orientation

In a previous post I indicated how to sketch a picture of a monoidal graph (or multigraph). A monoidal graph consists of two sets Comp (the components) and Wire (the wires) and two functions dom, cod: Comp -> Wire* (where Wire* is the free monoid on the wires). If dom of a component has length n then the component has n (ordered) left-hand ports; if cod of a component has length m then the component has m right-hand (ordered) ports. The functions dom and cod say to which wire a port is attached.
This means that a component looks very like a traditional dual in-line chip.
I realised in writing that post that in fact the picture of the monoidal graph was missing something - the orientation of the chip. I did indicate the left and right hand sides of the chip by giving them a different shape,  but you need to know which is the first port on the left and that will determine the order of the other ports.

I remembered having this problem years ago building circuits. The manufacturers are not always careful to tell you which is the first port.  Try googling IC chip orientation and you will see that people have problems - sometimes there is a dot, sometimes you need to look at the labelling, sometimes there is a notch.

I think in future I will draw monoidal graphs by using rectangular components and a dot indicating the first pin on the left.



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