## 10 Charsets for CDC machines ¶

What is now Recode evolved out, through many transformations really, from a set of programs which were originally written in COMPASS, Control Data Corporation’s assembler, with bits in FORTRAN, and later rewritten in CDC 6000 Pascal. The CDC heritage shows by the fact some old CDC charsets are still supported.

The Recode author used to be familiar with CDC Scope-NOS/BE and Kronos-NOS, and many CDC formats. Reading CDC tapes directly on other machines is often a challenge, and Recode does not always solve it. It helps having tapes created in coded mode instead of binary mode, and using `S` (Stranger) tapes instead of `I` (Internal) tapes. ANSI labels and multi-file tapes might be the source of trouble. There are ways to handle a few Cyber Record Manager formats, but some of them might be quite difficult to decode properly after the transfer is done.

Recode is usable only for a small subset of NOS text formats, and surely not with binary textual formats, like `UPDATE` or `MODIFY` sources, for example. Recode is not especially suited for reading 8/12 or 56/60 packing, yet this could easily arranged if there was a demand for it. It does not have the ability to translate Display Code directly, as the ASCII conversion implied by tape drivers or FTP does the initial approximation. Recode can decode 6/12 caret notation over Display Code already mapped to ASCII.

### 10.1 Control Data’s Display Code ¶

This code is not available in Recode, but repeated here for reference. This is a 6-bit code used on CDC mainframes.

    Octal display code to graphic       Octal display code to octal ASCII

    00  :    20  P    40  5   60  #     00 072  20 120  40 065  60 043
    01  A    21  Q    41  6   61  [     01 101  21 121  41 066  61 133
    02  B    22  R    42  7   62  ]     02 102  22 122  42 067  62 135
    03  C    23  S    43  8   63  %     03 103  23 123  43 070  63 045
    04  D    24  T    44  9   64  "     04 104  24 124  44 071  64 042
    05  E    25  U    45  +   65  _     05 105  25 125  45 053  65 137
    06  F    26  V    46  -   66  !     06 106  26 126  46 055  66 041
    07  G    27  W    47  *   67  &     07 107  27 127  47 052  67 046
    10  H    30  X    50  /   70  '     10 110  30 130  50 057  70 047
    11  I    31  Y    51  (   71  ?     11 111  31 131  51 050  71 077
    12  J    32  Z    52  )   72  <     12 112  32 132  52 051  72 074
    13  K    33  0    53  $   73  >     13 113  33 060  53 044  73 076
    14  L    34  1    54  =   74  @     14 114  34 061  54 075  74 100
    15  M    35  2    55      75  \     15 115  35 062  55 040  75 134
    16  N    36  3    56  ,   76  ^     16 116  36 063  56 054  76 136
    17  O    37  4    57  .   77  ;     17 117  37 064  57 056  77 073

In older times, `:` used octal 63, and octal 0 was not a character. The table above shows the ASCII glyph interpretation of codes 60 to 77, yet these 16 codes were once defined differently.

There is no explicit end of line in Display Code, and the Cyber Record Manager introduced many new ways to represent them, the traditional end of lines being reachable by setting `RT` to ‘`Z`’. If 6-bit bytes in a file are sequentially counted from 1, a traditional end of line does exist if bytes 10*n+9 and 10n+10 are both zero for a given n, in which case these two bytes are not to be interpreted as `::`. Also, up to 9 immediately preceeding zero bytes, going backward, are to be considered as part of the end of line and not interpreted as `:`14.

### 10.2 ASCII 6/12 from NOS ¶

This charset is available in Recode under the name `CDC-NOS`, with `NOS` as an acceptable alias.

This is one of the charsets in use on CDC Cyber NOS systems to represent ASCII, sometimes named NOS 6/12 code for coding ASCII. This code is also known as caret ASCII. It is based on a six bits character set in which small letters and control characters are coded using a `^` escape and, sometimes, a `@` escape.

The routines given here presume that the six bits code is already expressed in ASCII by the communication channel, with embedded ASCII `^` and `@` escapes.

Here is a table showing which characters are being used to encode each ASCII character.

    000  ^5  020  ^#  040     060  0  100 @A  120  P  140  @G  160  ^P
    001  ^6  021  ^[  041  !  061  1  101  A  121  Q  141  ^A  161  ^Q
    002  ^7  022  ^]  042  "  062  2  102  B  122  R  142  ^B  162  ^R
    003  ^8  023  ^%  043  #  063  3  103  C  123  S  143  ^C  163  ^S
    004  ^9  024  ^"  044  $  064  4  104  D  124  T  144  ^D  164  ^T
    005  ^+  025  ^_  045  %  065  5  105  E  125  U  145  ^E  165  ^U
    006  ^-  026  ^!  046  &  066  6  106  F  126  V  146  ^F  166  ^V
    007  ^*  027  ^&  047  '  067  7  107  G  127  W  147  ^G  167  ^W
    010  ^/  030  ^'  050  (  070  8  110  H  130  X  150  ^H  170  ^X
    011  ^(  031  ^?  051  )  071  9  111  I  131  Y  151  ^I  171  ^Y
    012  ^)  032  ^<  052  *  072 @D  112  J  132  Z  152  ^J  172  ^Z
    013  ^$  033  ^>  053  +  073  ;  113  K  133  [  153  ^K  173  ^0
    014  ^=  034  ^@  054  ,  074  <  114  L  134  \  154  ^L  174  ^1
    015  ^   035  ^\  055  -  075  =  115  M  135  ]  155  ^M  175  ^2
    016  ^,  036  ^^  056  .  076  >  116  N  136 @B  156  ^N  176  ^3
    017  ^.  037  ^;  057  /  077  ?  117  O  137  _  157  ^O  177  ^4

### 10.3 ASCII “bang bang” ¶

This charset is available in Recode under the name `Bang-Bang`.

This code, in use on Cybers at Université de Montréal mainly, served to code a lot of French texts. The original name of this charset is ASCII codé Display. This code is also known as Bang-bang. It is based on a six bits character set in which capitals, French diacritics and a few others are coded using an `!` escape followed by a single character, and control characters using a double `!` escape followed by a single character.

The routines given here presume that the six bits code is already expressed in ASCII by the communication channel, with embedded ASCII `!` escapes.

Here is a table showing which characters are being used to encode each ASCII character.

    000 !!@  020 !!P  040    060 0  100 @   120 !P  140 !@ 160 P
    001 !!A  021 !!Q  041 !" 061 1  101 !A  121 !Q  141 A  161 Q
    002 !!B  022 !!R  042 "  062 2  102 !B  122 !R  142 B  162 R
    003 !!C  023 !!S  043 #  063 3  103 !C  123 !S  143 C  163 S
    004 !!D  024 !!T  044 $  064 4  104 !D  124 !T  144 D  164 T
    005 !!E  025 !!U  045 %  065 5  105 !E  125 !U  145 E  165 U
    006 !!F  026 !!V  046 &  066 6  106 !F  126 !V  146 F  166 V
    007 !!G  027 !!W  047 '  067 7  107 !G  127 !W  147 G  167 W
    010 !!H  030 !!X  050 (  070 8  110 !H  130 !X  150 H  170 X
    011 !!I  031 !!Y  051 )  071 9  111 !I  131 !Y  151 I  171 Y
    012 !!J  032 !!Z  052 *  072 :  112 !J  132 !Z  152 J  172 Z
    013 !!K  033 !![  053 +  073 ;  113 !K  133 [   153 K  173 ![
    014 !!L  034 !!\  054 ,  074 <  114 !L  134 \   154 L  174 !\
    015 !!M  035 !!]  055 -  075 =  115 !M  135 ]   155 M  175 !]
    016 !!N  036 !!^  056 .  076 >  116 !N  136 ^   156 N  176 !^
    017 !!O  037 !!_  057 /  077 ?  117 !O  137 _   157 O  177 !_

#### Footnotes

##### (14)

This convention replaced an older one saying that up to 4 immediately preceeding pairs of zero bytes, going backward, are to be considered as part of the end of line and not interpreted as `::`.