Normally a board and schematic will always be consistent as long as they have never been edited separately (in which case the message "No Forward&Back Annotation will be performed!" will have warned you).
When loading a pair of board and schematic files the program will check some consistency markers in the data files to see if these two files are still consistent. If these markers indicate an inconsistency, you will be offered to run an Electrical Rule Check (ERC), which will do a detailed cross-check on both files.
If this check turns out positive, the two files are marked as consistent and Forward&Back Annotation will be activated.
If the two files are found to be inconsistent the ERC protocol file will be brought up in a text window and Forward&Back Annotation will not be activated.
The ERC protocol file contains several sections that list the inconsistencies found. Each of these sections may or may not be present, depending on which inconsistencies have been found. Please do not be alarmed if you get a lot of inconsistency messages. In most cases fixing one error (like renaming a part or a net) will reduce the number of error messages you get in the next ERC run.
Parts not found in board: IC1 R7This section lists the names of the parts that are present in the schematic, but are missing in the board.
Elements not found in schematic: C33 D2This section lists the names of the elements that are present in the board, but are missing in the schematic.
The following sections are only present if the part and element names have checked out to be consistent:
Parts/Elements with inconsistent packages: IC12 R1This section lists the names of the parts/elements that are present on both schematic and board, but which have inconsistent packages. Packages are considered consistent if they contain an equally named set of pads/smds.
Parts/Elements with inconsistent values: R55 100k 47k C99 10n 10pThis section lists the names of the parts/elements that are present on both schematic and board, but which have different values. The second column lists the value of the part in the schematic, the third column lists the value of the element in the board.
The following sections are only present if the part and element packages have checked out to be consistent:
Pins/Pads with different connections: Part Gate Pin Net Pad Signal IC5 A 2 GND 2 S$42 R3 R 1 D1 1 D2This section lists the names of the pins and pads that are connected to different nets/signals in schematic and board. The Net column contains the net name in the schematic, while the Signal column gives the signal name in the board. If either of these two entries is blank, this means that the pin/pad is not connected.
Making a Board and Schematic consistent
To make an inconsistent pair of board and schematic files consistent, you have to manually fix any inconsistency listed in the ERC protocol file. This can be done by applying editor commands like NAME, VALUE, PINSWAP, REPLACE etc. After fixing the inconsistencies you must use the ERC command again to check the files and eventually activate Forward&Back Annotation.
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