Wednesday, April 10, 2013

ALU board layout update

Since I've moved the Instruction Decode board along a good way, I decided the Arithmetic/Logic Unit board needed some attention.

Part of the problem with putting a project on hold like I sometimes do is that all the details of where you left off get flushed from mental cache, and it can take a half an hour or more just to figure out what needs doing. With the ALU board it appears I'd left off with only 21 FETs and 10 resistors unplaced, but almost nothing had been routed. With that figured out I settled in to place the rest.

I thought someone out there might want to see what my screen looks like doing this. I have a 30-inch, high-resolution (2650x1600 pixels) monitor, which allows me to display both the active portions of the schematic and the board layout at the same time without having to squint.

Eagle Schematic and Board Layout views -- i4004 ALU board

In this screen capture, I've just selected transistor T0172, which highlights the part on both the schematic and board windows. The grid displayed on the board is 16 mil squares, which I've found to be about as tightly packed as I'd want to attempt with these parts and my skill level.

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