scott-tee transformer to develop the 3-phase stator voltage outputs (S1, S2, and S3) of the single-speed synchro transmission. D/S converters are designed with holding circuits that  retain  the  contents  of  the  BAM  words  between computer updates of BAM data. The synchro output of the D/S converter is continuous in nature, indicating a new rotor angle only when a BAM word received from the controlling computer contains anew angular value. DIGITAL-TO-DIGITAL (D/D) CONVERSION This section covers those forms of digital data handled by various shipboard data conversion devices. These  devices  are  used  to  convert  digital  data  from shipboard weapon, radar, and other subsystems to the voltage levels and formats acceptable to the CDS computers. The  types  of  data  converted  include  control  and status signals, ready digital (RD) data, demand digital (DD) data, demand digital interrupt (DDI) data, and digital  input  channel/digital  output  channel  (DIC/DOC) data. Control and Status Signals Control and status signals are discrete ac or dc signals that indicate or control a single function (on/off, true/false, and so forth) or condition in a subsystem. Signals transmitted by CDS equipment to another subsystem are referred to as control signals because they generally initiate an action in the receiving system. Discrete  signals  received  by  CDS  equipment  are referred to as status  signals  because  they  generally indicate the status of a condition or function in another subsystem. CONTROL SIGNALS.—   Control  signals  are generated  from  individual  bit  positions  in  a  control word. Each bit position of the control word represents one control signal. The individual bits from the control word are fed to relay circuits. A binary ONE will cause a relay closure to take place and an ac or dc signal to be generated from the appropriate supply voltage. A binary ZERO will cause the relay to de-energize, open its contacts, and prevent the voltage transmission. STATUS SIGNALS.—   Status signals are ac or dc voltages received from external subsystems. Each status signal is assigned to an individual bit position in a status word. The status bit becomes a binary ONE when a status voltage is sensed. Lack of a status voltage 13-13 signal causes the status bit to remain a binary ZERO. Status   words   are   sampled   periodically   by   the controlling  computer  to  determine  the  current  condition of the individual status signal bits. Ready Digital (RD) Data Ready digital (RD) data is 12-bit parallel digital data generated by the CDS radar azimuth converters (RACs). The data indicates the antenna or sweep position of each individual ship’s radar. This data is transmitted to the CDS computer as requested by the computer for program processing and tracking of radar contacts. Demand Digital (DD) Data Demand digital (DD) data is parallel digital data input from manual entry devices. Two input channels are normally used. Each channel may be used by up to eight daisy-chained devices. Each device is identified by an address in the input word. DD data is sampled periodically by the computer to test for operator entries. Demand Digital Interrupt (DDI) Data Demand digital interrupt (DDI) data is parallel digital data similar to DD data. The major difference is in the method of data entry. DDI devices cause an interrupt to be generated to the controlling computer when an entry is made from the applicable device. Digital Input Channel/Digital Output Channel (DIC/DOC) Data Digital  input  channel/digital  output  channel (DIC/DOC)  channels  are  multiplexed  parallel  digital computer channels used to increase the input/output capabilities  of  the  controlling  computer.  Up  to  four DICs and four DOCs are provided. The channels may be used for input only, output only, or input/output (I/O) with   external   peripheral   devices   or   computers depending on the mode or format selected. TOPIC  2—SHIPBOARD DIGITAL/ANALOG SYSTEM INTERFACES In  this  topic,  you  will  learn  about  specific equipments and groupings of equipments involved in the data inversion and interfacing process aboard ship. These  equipments  permit  nominally  independent