GB1486362A - Interface module for a digital data transmission system - Google Patents

Abstract

1486362 Digital data transmission SINGER CO 24 March 1975 12165/75 Heading H4P [Also in Division G4] An interface module 10 is provided for coupling a subsystem, e.g. a computer, a remote terminal, a sensor or an output device of a digital data transmission system to a data link P, the module being operable in either a "receive" or a "transmit" mode; in the "receive" mode multisection control words and data words are decoded 108, 110, 112 and the different sections of the control words are directed by means of logic circuitry to different ones of a set of logic elements 120, 122, 124 and 126 coupled in parallel to a common bus 114 leading from the decoder. Each control word has the format illustrated in Fig. 3 (not shown), and includes an address portion which is used to select the required subsystem by means of a comparator 150 coupled to the address register 120, and a word count portion which is used in conjunction with a word counter 152 coupled to the word count register 122 to indicate how many data words are to be expected following a control word. A single bit of each control word is fed to register 124 to set the module in either the "receive" or the "transmit" mode. The entire control word is stored in register 126, and the data words are stored in an I/O register 128. Further registers 130, 132 are provided for conventional checking and testing purposes, and a parity checking circuit 116 is also provided. The logic circuitry for dividing the control words into their various sections includes a read-only memory 134 controlled by timing signals from a timebase generator 176 and a counter 178. When the module 10 is set to its "transmit" mode, data words from I/O register 128 and portions of control words from the logic elements 120, 122, 124 and 126 are fed via a common bus 156 to be encoded 160, 162 and 164 and then sent via a pulse shaper 170 and amplifiers 172, 174 to the data link P for transmission. A plurality of interface modules such as 10 are coupled in parallel (Fig. 1, not shown) so that, in the event of failure of a logic element of a module, a suitable logic element of another module may be substituted therefor by means of selector circuits such as 10a, 10b. Each interface module is constructed using three integrated circuit chips 100, 102 and 104.