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I/O INTERFACE FORMATS
TYPE    E    (NATO    SERIAL)

Fire Controlman Volume 03-Digital Data Systems
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NTDS Input/Output (MIL-STD-1397) The NTDS input/output interface is probably one of the most versatile of formats because it is designed to  handle  either  parallel  or  serial  formatted  information, depending  on  the  type  of  computer  and  its  I/O requirements. This interface specifies three I/O control and data signal categories. We cover the first two under parallel and serial operations later in this topic. The categories   include: Category  I  —Computer  to  external  device Category   II    —Computer   to   computer, intercomputer (IC) Category III —External device to external device Within this standard, there are nine types of formats (A through H and J). They include both serial and parallel   formats   as   described   in   the   following paragraphs. TYPE A (NTDS) SLOW. —Type A transfers parallel data of up to 41,667 words per second on one cable. This type interface uses 0 vdc (logical 1) and -15 vdc (logical 0) to transmit bit groupings of 16,30, or 32 bits, depending on the type of computer. The relatively large voltage change between logic states, with its inherent   time   delays,   limits   the   speed   of   data transmission. Type A can transmit digital signals up to 1000 feet. It is most frequently used in large mainframe and some minicomputers to interface with equipment found   in   the   data   processing,   display,   and communication subsystems. Type A uses a request and acknowledge protocol process. It transfers control and data words using two cables: one input and one output for the same channel. You may, however, encounter a few devices that use input only or output only portions of an NTDS slow channel. Type A signal designations for input and output include the following: EIE  —External  interrupt  enable IDR —Input data request EIR —Extemal interrupt request IDA  —Input  data  acknowledge EFR —Extemal function request EFA  —External  function  acknowledge ODR  —Output data request ODA  —Output  data  acknowledge TYPE B (NTDS) FAST.  —Type  B  transfers parallel data of up to 250,000 words per second on one cable. This type interface uses 0 vdc (logical 1) and -3 vdc (logical 0) to transmit bit groupings of 16, 30, or 32 bits depending on the type of computer. Type B can transmit digital signals up to 300 feet depending on the type of cable used. It is most frequently used in large mainframe or some minicomputers to interface with equipment found in the data processing, display, and communication subsystems. Type B uses a request and acknowledge protocol process. It transfers control and data words using two cables: one input and one output for the same channel. You may, however, encounter a few devices that use input only or output only portions of an NTDS fast channel. Type B uses the same input and output signal designations as type A. TYPE C (ANEW). —Type C transfers parallel data of up to 250,000 words per second on one cable. This type of interface uses 0 vdc (logical 1) and +3.5 vdc (logical 0) to transmit bit groupings of 16, 30, or 32 bits, depending  on  the  type  of  computer.  Type  C  can transmit  digital  signals  up  to  300  feet  depending  on  the type of cable used. It is most frequently used in large mainframe or some minicomputers to interface with equipment found in the data processing, display, and communication subsystems. Type C uses a request and acknowledge protocol process. It transfers control and data words using two cables: one input and one output for the same channel. You may, however, encounter a few devices that use input only or output only portions of an NTDS ANEW channel. Type C uses the same input and output signal designations as type A. TYPE    D    (NTDS    SERIAL).    —Type     D asynchronously  transfers  serial  data  using  a  10 megabits per second (Mb/s) clock rate over a single coaxial  cable.  Two  cables  are  required  for  bidirectional communications,  a  source  line  (computer  to  peripheral) and a sink line (peripheral to computer). The source line  is  used  to  transmit  data  and  external  functions, while the sink line is used to transmit input data and external   interrupt   codes.   Type   D   transfers   are accomplished using two types of bipolar pulse trains: (1) control frames and (2) control and data words. The actual input or output data is transmitted in 32-bit information  frames.  Control frames are three bits in length, a sync bit followed by two control bits. The signals required for input transfer will occur on the input channel (input request, input enable, and not ready) and the signals required for output transfer will occur on the output channel (output request, output enable, and not ready). A binary 1 will be a pulse of phase zero degrees and will be a high polarity followed by a low polarity. 7 - 2 2






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