The DEC alphabet and IDC connectors
DEC used letters do designate pin numbers on connectors. Not all letters are used to prevent errors when letters look alike too much. The initial alphabet was:
A, B, C, D, E, F, H, J, K, L, M, N, P, R, S, T, U, V (18 pins, the size of a flipchip connector).
Later extended with W, X, Y, Z as well to support 40 pin BERG/IDC connectors. Helpfully, BERG connectors using this scheme number starting from the bottom left corner, while IDC starts at the top right corner. Great.
A mapping for IDC <-> BERG follows below:
| Berg | IDC |
|---|---|
| A | 40 |
| B | 39 |
| C | 38 |
| D | 37 |
| E | 36 |
| F | 35 |
| H | 34 |
| J | 33 |
| K | 32 |
| L | 31 |
| M | 30 |
| N | 29 |
| P | 28 |
| R | 27 |
| S | 26 |
| T | 25 |
| U | 24 |
| V | 23 |
| W | 22 |
| X | 21 |
| Y | 20 |
| Z | 19 |
| AA | 18 |
| BB | 17 |
| CC | 16 |
| DD | 15 |
| EE | 14 |
| FF | 13 |
| HH | 12 |
| JJ | 11 |
| KK | 10 |
| LL | 9 |
| MM | 8 |
| NN | 7 |
| PP | 6 |
| RR | 5 |
| SS | 4 |
| TT | 3 |
| UU | 2 |
| VV | 1 |
(40 pin)
| WW | | | XX | | | YY | | | ZZ | |