Patent GB-1409197-A (GB)
Title: Systems for transferring bits between a plurality of asynchronous channels and a synchronous channel
IPC: H04L5/24
Filed: 1973-04-09
Abstract: 1409197 Digital transmission; time division multiplexing COMPAGNIE EUROPEENNE DE TELETKANSMISSION 9 April 1973 [11 April 1972] 17003/73 Heading H4P A system for transferring bits from K asynchronous channels carrying up to n bit characters to a time division multiplex synchronous channel comprises K one bit terminal memories and a storage circuit having a n capacity coupled to the synchronous channel. An intermediate circulating memory has K.C compartments, C being an integer greater than one, each comprising n cells, also auxiliary one bit cells storing bits indicating occupancy. The circulating memory also comprises n shift registers for the circulation of compartments. An address circuit receives clock pulses for allocating groups of C successive compartments in the intermediate memory and assigns K groups to K first terminal memories. A device coupled to the internal memory and address circuit controls bit transfer between each one of K first terminal memories and the assigned group of data compartments, also the character by character transfer of bits between each of the groups of compartments and the terminal memory, the control device including means causing bit transfers into the first compartment, not occupied, of each of the groups of compartments, and also into the first stages of the shift registers. The device also causes output bit transfers from the first compartment of a group and from the last stages of the shift registers and when such transfer makes the first data compartment of a group wholly available causes the transfer of the contents of each one of the other compartments to the preceding compartment. The diagrammatically illustrated circulating memory Fig. 1 has, for example, three sections respectively assigned to asynchronous channels 301-303 and is subdivided into a data memory 31, occupation memory 32 and position memory 33.  Bits are sampled one by one and are recorded similarly in the data memory, successive bits being recorded in successive cells of a compartment. When a character has been completely recorded all bits are simultaneously transferred to an output storage circuit which directs bits to the time channel assigned to the asynchronous channel. Other sections are then shifted forward one section in the same group. Fig. 5 shows part of the circulating memory R1 (R2-R8 not shown) together with the occupation register Ro and the first position number register R1, (R2, R3, not shown); all these registers receive shift pulses IM. Section content switching AND gates 52, 62, 72 transfer the last three sections of a memory group to the preceding section of the same group upon a character being transferred from the first section of a group, the arrangement including "write in" AND gates 54, 64, 74 and "loop AND gates" 53, 63, 73, outputs from the latter being connected to OR gates 51, 61, 71 respectively. The "write in" gate, e.g. 54 of register R1 is supplied with a signal B, formed by a succession of data bits, from input storage circuits. AND 55 receives a "write in" signal M from control circuit (16) (Fig. 2, not shown) and an input from a decoder 29 receiving output signals r1-r3 from the last stages of the three position number registers defining the position r of the first empty cell in the memory section. Common adder 30 also has inputs r1-r3 plus input M with outputs to position number gates, e.g. 74. All registers operate in a circulating mode with the output connected back to the input through a gate, e.g. 53 except when a bit is to be inserted; gate 53 also receives an input from NOR 56 receiving a transfer signal D and an input from gate 55. The circulating memory (10) is incorporated in the arrangement of Fig. 2 (not shown) in which input storage circuits (11-13) receive inputs from asynchronous lines (1-3) and a clock (5) produces pulses at a frequency mFc where m is an even integer, e.g. 16, and Fe is the L.C.M. of the input frequencies; clock 5 is followed by a divider circuit 15 which supplies pulses to (11-13). Another clock of frequency FM is applied to the registers of the circulating memory also to a MOD-4 counter 7 followed by a MOD K=3 counter 8 having a double output to decoder 23 and control circuit (16) which is connected to circulating memory (10) and output storage circuit (14).  Detailed arrangements of the various parts of the circuit are described in the Specification.