With schematics of digital systems, my preferences are:
- For groups of similar circuits, such as address lines, data lines; use a bus structure. One bus for each different group. With individual lines fanning out to each chip including an appropriate label. This is especially important when mixing address or data lines to RAM chips (the processor A0 line does not have to go to the RAM A0 pin for example).
- For individual signals, that go point to point, that is one singe source to one single destination, where practical, draw these as lines. Where not practical to do so, use labels that include the details of from/to. So for example: “RAMCS (from IC6)”. If a signal crosses to another sheet/page, include the sheet/page number.
- For signals that go from one source to a handful (two to five) places, again, where practical, draw these as lines. Where not practical to do so, fan out the lines to individual labels that include the details of from/to.
- For a signal that goes to many places (more than five), but which is not part of a group, such as a clock, use simple labels. But include a note on the diagram that lists all the chips that connect to said signal. This also applies to auxiliary or secondary power supply lines.
- For the main supply line and the main 0V/ground/common, use the appropriate power/ground symbols. However, where possible, draw the relevant decoupling capacitor next to the chip it is physically intended to decouple.
The reason why I do it this way is simple. It makes fault finding a whole lot easier, especially if you come back to it some time after originally drawing it. It’s the hardware equivalent of well commented source code.
There is nothing worse than spending a large chunk of time scanning multiple sheets/pages or a large diagram looking to find a signal tag and not being able to find it. Or worse, with a signal used in multiple places, looking for one that you expect, but can’t find, because it does not exist…
Mark
Login
Register
FAQ
Search
