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quiz:3h7e0f4_io_data [2016/01/02 23:20] (current)
mcmaster created
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 +====== Inputs and outputs ======
 +
 +In the previous module you came up with the pin numbering scheme and identified power and ground. ​ Now we'll go a little deeper to figure out data flow.
 +
 +  * Identify the circle containing ESD protection
 +    * Detail
 +      * {{:​quiz:​metal_gate_cmos:​esd_q.jpg?​600|}}
 +    - A
 +    - B
 +    - C
 +    - D
 +    - E
 +    * [1]
 +    * (1)
 +    * Many chips use large parallel diodes for ESD protection and so this ones a little different. ​ However, ESD protection can often be identified by virtue of a component that attaches to both VDD and VSS.  While some of the transistors do this, they have logical connections that indicate they have a higher purpose. ​ ESD protection on the other hand tends to be very simple and regular. ​ Looking at the components in A I believe they are resistors as seen with NMOS logic (ex: see Intel 4004 die photos and Flylogic analysis). ​ Presumably this provides a more favorable conductive path and shunts away from the input gates.
 +      * B is a transistor
 +      * C is a transistor
 +      * D is a bond wire (ball bond)
 +      * E just has more metal and metal doesn'​t typically help ESD.  It can on larger chips when its used as a capacitor between VDD and VSS
 +
 +  * Identify inputs
 +    * Detail
 +      * {{:​quiz:​metal_gate_cmos:​iodir_q.jpg?​600|}}
 +      * ie not outputs or power/​ground
 +    - A
 +    - B
 +    - C
 +    - D
 +    - E
 +    * [1|4|5]
 +    * (1)
 +    * Anything with a fat transistor near the pad not connected to a gate is a pretty clear output or possibly tri-state. ​ I highlighted a gate on each questioned input, although keep in mind that simply having a gate attached to a pin doesn'​t make it an input as the circuit can have feedback or tri-state (necessary but not sufficient). ​ Going through each pin you see that each is either connected to only gates or only source/​drain. ​ We can now identify all pins as either power, input or output. ​ D had to be traced to the other side of the die and is the lowest circled gate.
 +      * {{:​quiz:​metal_gate_cmos:​iodir_a.jpg?​600|}}
  
 
quiz/3h7e0f4_io_data.txt ยท Last modified: 2016/01/02 23:20 by mcmaster
 
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