Service manual

6
If we always split the binary codes into groups of four, the conversion remains easy :-
8 4 2 1 8 4 2 1 8 4 2 1
1 0 0 1 1 1 1 1 0 0 0 0 = 9 F 0
1 1 1 0 1 0 1 0 1 0 0 1 = E A 9
0 0 0 1 0 1 0 1 0 0 1 = A 9
If you can count up to sixteen you can use Hexadecimal!
Conversion Tables
Now look at a table which shows part of the Eprom contents for a typical conversion. All
numbers are in Hexadecimal. Each box actually contains an eight bit binary code which is
shown as a 2 digit HEX number because otherwise the page isn't wide enough!
0 1 2 3 4 5 6 7 8 9 A B C D E F
000 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF 0F
001 10 11 FF 13 14 15 16 FF 18 19 1A 1B FF 1D 1E 1F
002 20 FF 22 23 24 25 FF 27 28 29 2A 2B 2C 2D 2E 2F
003 30 31 32 33 34 35 36 37 38 39 3A 3B FF FF FF FF
004
005 Out of this block of sixty four boxes, only forty are
006 selected by the channel switch whose codes range from 0F to
007 3B (HEX). The unused boxes in an Eprom are usually FULL, not
008 empty, and produce 1 1 1 1 1 1 1 1 on the output pins. This
009 table has been arranged so that the contents of each box
00A are identical to the channel switch code which selects it.
00B For instance the switch code 2A selects the box whose
00C contents are also 2A. This is because, in most conversions,
00D we want to KEEP the existing channels as well as to add new
00E ones. The new channels will be added in another block thus :-
00F
010 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF 3C
011 3D 3E FF 40 41 42 43 FF 45 46 47 48 FF 4A 4B 4C
012 4D FF 4F 50 51 52 FF 54 55 56 57 58 59 5A 5B 5C
013 5D 5E 5F 60 61 62 63 64 65 66 67 68 FF FF FF FF
These codes continue where the original ones ended so the box selected by switch code 1F
is 3C. Note that the switch can only select 40 channels and will normally use six of the
Eprom input pins to do this. An Eprom has more than six inputs, however, and any of
these can be used to select another bank of 64 boxes.
Note, also, that five boxes are not used. These represent the "A" channels, "hops" or
"skips" in FCC rigs. The Eprom can, of course, be programmed so that these channels are
included, at the expense of losing five other channels in this bank, since the channel switch
can select only forty in any one bank of 64.