DEC edge connector contact identification

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The edge connector contact groups of DEC cards such as FLIP CHIPs on the edge of a hex card are 'numbered' A-F (for smaller cards, see below). The groups are often called 'rows' in DEC documentation; the term 'slots' is also used, but this is confusing, because backplanes also have numbered slots for cards, numbered horizontally. The term 'connector' is also seen.

The groups are 'numbered' starting from the top (when the card is installed, vertically), with 'A'; this would be the right-hand edge, when the card is horizontal, with the component side up, and the connector 'fingers' toward the viewer. Shorter cards (quads and duals) use subsets of these, also starting with 'A'.

Within each row, the individual contacts are 'numbered' from the DEC Alphabet; those on the component side are further numbered '1', and those on the solder side (for boards with contacts on both sides - not all do), '2'. I.e. with the board in a horizontal position, as described above, the right-most contact on the top side (i.e. visible) would be identified as 'AA1'.

For smaller cards (quads and duals), DEC used two contradictory systems: one, which we can call 'board-centric', identified the top connector (on boards of any size ) as 'A', and continued in alphabetic sequence from there; the other, which we can call 'slot-centric', identified the connectors by the slot connector into which it plugged. (The RK11-D engineering drawings actually have a page which shows both systems applied to one of the RK11-D's quad cards.)

The apparent reason for the use of two contradictory (and thus potentially confusing) systems is that the slot-centric system works better for cards destined for a unique, fixed slot in a single type of backplane; the board-centric system is better for cards like early FLIP CHIPs, which were generic, and appeared in different locations on different backplanes.

See also