718 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1956 



card translator mechanism ; each of these mechanisms contains an identi- 

 cal repertory of translations. Each decoder also has available, through 

 connectors, a common pool of translators containing a large quantity of 

 less-often used information. In order to better understand the duties 

 that a magnetic drum translator must be expected to perform it will now 

 be convenient to follow, in a highly abbreviated manner, a typical opera- 

 tion of the decoder and its associated card translator. 



The first translation on an incoming call is performed using the first 

 three decimal digits accumulated by a sender. As soon as three digits are 

 available the sender connects to a decoder which immediately signals its 

 individual translator to perform certain mechanical chores in preparation 

 for selecting a card. There are several sequencing signals between the de- 

 coder and translator during the complete cycle of a translation (several 

 of these signals must be synthesized by the drum translator); acting 

 on one of these signals from the translator, the decoder passes the input 

 code from the sender, adding certain supplemental information of its own. 



The three decimal digits of the input code are in checkable combina- 

 tions of two leads energized in each of three groups of five leads connected 

 to the translator. The supplementary information supplied by the de- 

 coder is in a similar checkable combination on six leads. None of the re- 

 maining leads in the total of 38 is energized, since the translation being 

 described involves only three code digits. 



In the translator, the input code actuates the card selecting mechanism 

 and also operates relays whose contacts are wired with a checking net- 

 work which confirms that the input code, and the responsive operation 

 of the code bars, is an authentic combination. This is done by establish- 

 ing a path to operate a "code bar check" relay, cbk. (This relay retains 

 the same identity in the magnetic drum translator.) 



Acting upon the authenticity check, the card translator proceeds to 

 select a card, and signals the decoder to begin timing for a possible non- 

 appearance. When the card is in a position to be read, the decoder is sig- 

 naled on two "index" channels, ind. The decoder now "reads" the card 

 by applying 130 volt battery to the coils of its register relays; the re- 

 quired relays operate through the ionized cold-cathode gas tubes in the 

 translator, and lock up, extinguishing the gas tubes. 



'{'he first card dropped may provide information sufficient for complet- 

 ing the connection; in this circumstance the decoder will then call in a 

 marker. The first card, however, may specify that more digits are re- 

 quired and the decoder will so instruct the sender. The sender, unless it 

 already has the necessary digits, is then dismissed by the decoder which 

 also instructs the translator to restore itself to normal. 



