602 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



coding elements to be selected or causing the same coding element to 

 produce different output codes. 



For instance, in Fig. 4, the input code, consisting of a mark on one of 44 

 leads, causes the translator switch to select one of the 44 possible positions 

 and the various terminals contacted in this position and their associated 

 changeable cross connections constitute the coding elements to mark the 

 required output code leads. The output code for any input code can be 

 changed by changing the cross connections in the coding element. In this 

 case they can also be changed by moving the "stop-point" cross connection 

 to a new stop point causing a new coding element to be selected. (This 

 permits numerous inputs to have the same output.) 



Now, in the case of Fig. 5, the same general situation exists, each coding 

 element consisting of a route relay with changeable output connections and 

 with provision for changing the relay selected by the input code. 



We can now go on to examine some of the variations of this general 

 scheme in practice and theory. 



Number Group Translator for $5 Crossbar Office 



Figure 6 shows the changeable translator used in the # 5 Crossbar System 

 to determine the equipment location number when the called directory 

 number is known. This translator is arranged to handle 1000 directory 

 numbers, but is not limited to this capacity. 



The input code is a 3-place decimal number. The output is a mixed base 

 number coded by one mark in each of six groups of code marking leads. 



The operation here is preceded by the selection of the correct translator 

 according to the thousands digit of the called pumber. Then the input code 

 causes the relay tree to select (for three wires) a 3-point directory number 

 terminal each point of which is connected to a coding element furnishing 

 two items of output information. 



The economy of this arrangement lies in the use made of resistances for 

 the output coding elements. This is a sample of what has come to be known 

 as passive-element coding, which will be further illustrated later. 



The difficulty the designers faced in this case was that each translator, 

 while having only 1000 possible inputs, must provide for translation to a 

 very large number of possible outputs, each different and each consisting 

 of a mark on six different leads. If the scheme of Fig. 4 had been employed, 

 then the translator switch would have required provision for 1000 positions 

 and 6000 wires. If the scheme of Fig. 5 had been used, then a total of 1000 

 coding relays would have been required and each coding relay would have 

 had six contact sets and cross connections. 



By employing a relay selecting tree carrying three wires and using three 



