Patent GB-1478363-A (GB)
Title: Data transmission systems
IPC: G06F13/22
Filed: 1974-07-30
Abstract: 1478363 Data transmission; master and slave systems MULLARD Ltd 30 July 1974 33587/74 Heading H4P Apparatus locally interfacing a computer with each of a plurality of bi-directional serial channels connected to remote terminals coinprises individual channel buffers storing a single input parallel data word received serially from its respective remote terminal with means for sequentially polling each buffer, which polling means is arrested at the presence of an input data word in a buffer to stop the polling at that buffer, each buffer being responsive to a RELEASE signal from the computer indicative that the computer has received an input data word to clear the buffer, and the polling means being responsive to said RELEASE signal to re-start the polling at the next buffer. An acknowledge word is transmitted serially on the channel from whose buffer a data word has just been received by the computer so as to inform the remote location that it may send another data word. The polling arrangements may comprise a buss from which input words are extracted by serially imposed addresses. At least one of the remote terminals may have an interface connecting to a group of data sources, and one of the terminals may be a further computer mutually active processively with the first computer. Computer CP1, which may be a small foreground computer and computer CP2 which may be a large central computer are connected to each other and a plurality of remotely located interfaces RC1 etc., through interfaces LC1, LC2 etc., by duplex 2 wire channels; data sources and sinks, e.g. laboratory terminals, DIN, DOP may be linked to respective interfaces by individual sub channels. These are polled by an input multiplexer IMX and when a sub channel is addressed having data available polling stops and one data word is sent through transmitter-receiver over channel LM1 to interface LC1 and is placed parallelly in buffer TRL1. Buffers TRL are polled in turn and when in TRL1 computer CP1 has received the word, an acknowledgement is sent back to remote interface RC1 which allows multiplexer IMX to resume polling input sub channels. If computer CP1 has information to send to one of data sinks DOP multiplexer OMX routes it according to its address. Buffers DES1 etc., each store one word and are polled in turn by a module by distributer MX which is arrested at each buffer which has a word stored in it. When the computer has injected the word release line 17 is activated causing serializer SER to transmit an acknowledgement word via line 15, 16 and the sender of TRL1 etc., associated wth the appropriate buffer; the appropriate buffer is also cleared. Where information transfer is required between LC1 and LC2 an inhibit line 19 is activated so that MX stops at the buffer connected to LC2 and an output word sent to LC2 which will acknowledge hence buffer DESC will be cleared ready for an input word. Since intercomputer links may be used to transmit programmes as well as data the processing power may be distributed between them. The terminals RC1 etc., may received experimental data and provides equitable use of a computer between experiments which may have considerable data to process and those which have much less. Detailed arrangements of the various parts of the system are given in the Specification. Code checking may be employed which provide an invalid signal where appropriate and a modified acknowledge word to be sent.