TRANSLATORS AND IDENTIFIERS IN SWITCHING SYSTEMS 611 



coding elements consist of steel cards, notched at the lower edge according 

 to the input code. The output code is carried on the card in the form of 

 small and large holes. 



The coding elements (cards) are selected, as in the sHde bar translator, 

 by selecting code bars that will drop the required card. Reading is done by 

 photo cells (actually photo-transistors) which detect the presence or absence 

 of light through the tunnels formed by the holes in the stacked cards. 



Pre-translator for No. 5 Crossbar System 



This all-relay translator is used for obtaining one of three possible sets of 

 switching instructions at a time when it is impractical to consult the more 

 complete office code translator associated with the marker in this system. 



Provision is made for 576 possible input codes on a 3-place decimal 

 basis each translatable to one of only three possible output codes each 

 consisting of a mark on one of three output leads. 



Because of these restricted capabilities it will not be illustrated here,' 

 but its general principles are worth noting because it is an example of how 

 close tailoring to the requirements can effect economy. This translator is 

 one of the few examples of changeable tianslators which do not follow the 

 general principle used in the previously described translators of this type. 

 That principle, it will be recalled, is that each input code causes the selection 

 of an individual coding element which determines the output code and 

 changes are made by causing the selection of different coding elements or 

 by changing the output of the coding elements. 



In this pre-translator the input codes are teamed in groups of three, each 

 of the group causing the selection of the same code point terminal. Hence 

 only one third as many code point terminals are required as there are 

 inputs. Each of these code point terminals is cross connected to one of 27 

 terminals, each of which represents a different permutation of each of the 

 three possible outputs. At this terminal three possible answers are repre- 

 sented, and three relays beyond this point select the correct answer, de- 

 pending on whether or not the input code is the first, second or third of the 

 group of three. 



Changes for any input code are made by changing the jumper affecting 

 this code and its two associated codes to a new terminal representing the 

 new permutation. 



This arrangement reduces the required number of relay contacts, cross 

 connections and cross-connecting terminals as compared to the number 

 required by more conventional all-relay translators. It would become im- 



^ For a full description, see Pre-translation in No. 5 Crossbar, R. C. Avery, Bell Labora- 

 tories Record, April 1950. 



