At 05:09 AM 8/14/2003, Edi Im Hof wrote:
It's also a good idea to set the ERC a bit tighter. [...]

On intentionally left open pins, I place a "no erc mark" on it. Keystrokes p-i-n, witch is easy to remember because you'll place them on a pin.

I have found quite a lot of schematic errors this way.

I'd like to underscore this. Especially when one is new to Protel, and is faced with a host of mostly phoney errors, it's tempting to set the ERC to tolerate open pins and type incompatibilities. And it's a bad idea.


As to unconnected pins, when you deliberately leave a pin open, it is very simple to place a No-ERC directive on it. You'll never have to look at it again. And if you forget to do this, you'll get a warning and you can quickly and easily fix it. The large majority of schematic errors leave an unconnected pin.

Years ago, designing with mylar and tape, I had an engineer who used to take a design and quickly go over it for unconnected pins. Even on a complex multilayer design (complex for those days might have meant 6 layers), it was easy to see this. And then he'd make sure that they were all properly unconnected. He'd find the bulk of errors very quickly with this....

As to other errors, many types of pin type combinations will generate an error with the default matrix. The best solution may be to fix the pin types, i.e., make, for example, a connector pin be an input or an output or passive instead of I/O, which doesn't like to be connected to an output. But this is not always practical. so, once again, it's simple to place No-ERC directives, though in this case I'd wait until running the first ERC. If it is easy to understand why an error is popping up, it may be relatively safe to suppress it with No-ERC, but if it is at all unclear, the safe path is to figure out why the error is happening. You might just find an error. And once you know, and it is not practical to fix it -- i.e., the error is purely formal -- then it should be suppressed. It only takes minutes at most to deal with even a host of connector pins.

The goal is to generate a clean ERC report. Ideally, No-ERC markers would not be used, but practical reasons make us very glad that the primitive exists: at least we have made a conscious decision that a particular "error" or warning can be disregarded, and the markers allow us to avoid having to make this decision with every revision of the schematic.

The cost of a schematic error can be very high, both in terms of money and in time-to-market, so it's worth the effort to learn to use the error-checking tools to best advantage. In the end, it's easy, the difficulty is only in the beginning....

It's too bad that Protel 99SE does not have editable pin types at the schematic level: Tango DOS allowed this.... (In Protel, pin types are only editable in the Library editor.) What I'd have liked to see would have been a symbol attribute that is "Allow Pin Electrical Type Edits." If checked in the library, the pin types would be editable at the schematic level. If not, they'd be locked. So a connector symbol, generally, would have editable pin types. And then the error checking could get even better. I'd also like to have a way to quickly see the pin type of a pin. (Again, this was easy in Tango DOS).

Has any of this been done in DXP?




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