I thought I could read schematics, but I have this problem: sometimes there are unnamed signals connected to buses and I don't know where they are supposed to be connected.
Example:
IC3 pis 14...23 IC1 pins 12...19
How to read those?
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1\$\begingroup\$ Indeed, that is a poorly formed schematic with improperly defined bus(es). Do not use this print as an example of a proper schematic representation. You should question and confirm everything. 2 demerits for bhabbot.net.nz \$\endgroup\$– Chris KnudsenFeb 6, 2019 at 15:43
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\$\begingroup\$ You should download the Eagle CAD project and work from that, you can get info on each net a whole lot better than you can from an image. But yes, this is poor design, every net should be named and labelled, especially if connecting into a bus like that. \$\endgroup\$– Ron BeyerFeb 6, 2019 at 18:26
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\$\begingroup\$ I figured it all out by looking at the original GALblast schematics (I can't check the project files ATM). Anyway, good to know it's not me, as it's not the first time I see schematics with such problems. Thanks everyone. \$\endgroup\$– Al JolsonFeb 6, 2019 at 19:42
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1 Answer
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You're right, it isn't clear. It would be interesting to see the netlist produced from that schematic.
However, we can infer a few things about the application.
It's a "GAL/ATF Blaster", and it would seem that IC1 and IC3 are the sockets into which you put the device being "blasted". Only one will be occupied at a time.
Furthermore, the O[0..9] bus is simply connected to a pack of pulldown resistors, and the only purpose seems to be to ground the unused outputs on the device being programed.
Therefore, it's probably safe to assume that each pin gets its own pulldown, and that it's safe to connect the same pulldown to a pin on both sockets.
answered Feb 6, 2019 at 14:35
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\$\begingroup\$ The fact they are not named does indeed imply that the designer did not care for those signals at all, so neither should we. Good decision by an experienced designer, or bad decision from a novice designer; how to tell the difference? \$\endgroup\$ Feb 6, 2019 at 17:45