limit to maximum limit). Binary codes of ONES and ZEROS are used to represent digital values. Each bit position in a binary number represents a portion of the overall quantity being represented. The summation of the values of the set bits (ONES) determines the value to be represented. ANALOG-TO-DIGITAL (A/D) AND DIGI- TAL-TO-ANALOG  (D/A)  CONVERSIONS—  The analog-to-digital  conversion  process  can  be  divided into  three  operations: sampling,  quantization,  and encoding. ANALOG AND DIGITAL QUANTITIES— An analog signal is sampled or tested repeatedly over a period of time to determine the characteristic that contains  the  analog  quantity.  The  sampled  analog  value is converted to the nearest binary value or quantity. The binary value is then encoded into a code acceptable to the digital equipments that use the data. Standardized binary   words   called   BAMs   (binary   angular measurement) are used to transmit angular, range, and height values between digital equipments in shipboard combat direction systems. Other coding systems such as Gray code or binary-coded decimal (BCD) are also used to transmit converted values. ANALOG-TO-DIGITAL CONVERTERS— An analog-to-digital converter is a device that receives an analog signal and converts it to a digital (binary) quantity with a given accuracy and resolution. SYNCHROS—  One of the most common analog shipboard signals indicating angular position that requires conversion to binary is the 3-phase or 5-wire synchro signal. Synchro is the name given to a variety of rotary, electromechanical, position-sensing devices. A synchro system is made up of a combination of a synchro transmitter and one or more synchro receivers. There  are  two  major  classifications  of  synchro  systems: torque systems and control systems. Most shipboard synchro systems operate on a supply or reference voltage of 115 vac at a frequency of 60 or 400 Hz. SYNCHRO  ACCURACY—  The accuracy of data transmitted  by  synchros  is  improved  by  using  a multispeed  synchro  system  such  as  a  dual-speed system.  A  dual-speed  synchro  system  uses  two  synchro transmissions,  with  a  common  reference  voltage,  called the coarse and fine transmissions. The coarse and fine transmissions are converted separately and the results are then combined into one BAM word. SYNCHRO  SIGNAL  CONVERSION—  Two methods  are  currently  in  use  to  convert  synchro  signals to digital (BAM) words: the sector method and the octant  method. SECTOR METHOD— The sector method first determines the 60-degree sector angle in which the rotor is  positioned  using  the  stator  voltages.  When  the  sector has been determined, two of the three stator voltages are sampled to determine the ratio angle within the sector. The sector angle and the ratio angle are then summed to determine the binary angle of the rotor position in BAMs. OCTANT  METHOD—  The octant method first determines the 45-degree octant by converting the synchro signal into two sine and cosine voltages. The remaining angle within the octant is determined by a process of successive approximations. THE  DIGITAL-TO-ANALOG  CONVERTER CV-2517B/UYK—  The CV-2517B/UYK DAC is a multipurpose digital-to-analog converter. It is capable of accepting parallel digital data words (BAMs) and converting them into linear, scalar, or synchro output signals. Each DAC is divided into two channels, designated channels A and B. Each channel can output two linear voltages, a sine/cosine scalar signal, or a single-speed synchro signal. SHIPBOARD DIGITAL/ANALOG SYSTEM INTERFACES—  Shipboard   digital/analog   system interfaces  permit  nominally  independent  shipboard systems  or  subsystems  to  communicate  or  interface with the combat direction system. MULTIPLEXING  DATA  CONVERTERS— Multiplexing  data  converters  are  computer-controlled multipurpose  devices  that  operate  between  one  or  more digital computers and a variety of control, status, digital and  analog  devices  located  in  remote  shipboard subsystems. KEYSET    CENTRAL    MULTIPLEXER (KCMX)—The   KCMX   provides   the   means   for exchanging  data,  control,  and  status  information between either one of two computers and a variety of I/O   devices.   The   KCMX   duplexer   allows   two computers  to  alternately  control  operation  of  the KCMX. Three external function (EF) commands are used to control the duplexer operation: REQUEST CONTROL,  RELEASE  LOCAL,  and  RELEASE REMOTE. The KCMX can operate in one of seven modes, as specified by the controlling computer: NEUTRAL, DUPLEX, RDUC (receive data from unit computer),  TDUC  (transmit  data  to  unit  computer), TDUC  and  RDUC,  INTERRUPT,  and  KEYSET ERROR. 13-40