different; but in addition, I/O operations include not only digital ICs, but also linear ICs. The linear IC circuits  are  the  first  and  last  type  of  circuitry  the information interfaces with when entering and leaving the computer. In this topic, we discuss some of the more common circuits you will encounter when dealing with I/O functions. In addition to the circuits we have discussed in the CPU and memory sections, you must be familiar with  driver and receiver  circuits  (linear ICs). Review chapter 4 of this volume and NEETS, Module 13, Introduction to Number Systems and Logic Circuits. They provide excellent reviews of the circuits and  their  functions  covered  in  the  remainder  of  this topic. l l l l l l l l The circuits include: Adders Command signals (enables) Decoders Line drivers and receivers Registers (includes RTC and Monitor Clock for IOCs) Selectors Timing Translators One  of  the  primary  uses  of  registers  in  I/O operations  is  to  provide  the  interfacing  between  the CPU, I/O, and memory. They enable and route control and data information  between  the  CPU,  I/O,  and memory using the internal bus system. In a computer with no I/O processor, a register will be designated as either an input or output register (fig. 7-11). Decoder circuits  are  used  for  address  translation,  control  circuits for  governing  the  operation  of  the  interface,  data registers,  and  status  registers  for  information  exchange. The data registers are used to hold or  buffer data  during interchanges between the very fast CPU and the slower external   equipments. The  status  registers  hold information for the CPU that indicates the operating condition  and  current  activities  of  the  external equipments.  We  discuss  external  interfacing  later  in this  topic. INPUT/OUTPUT  FUNCTIONS The input and output functions performed by an I/O processor   are   defined   and   enabled   through   the interpretation and execution of input/output and/or input/output  controller  (I/O(C))  commands  obtained from main memory. The I/O circuits provide the Figure  7-11.—Computer  operations  with  no  I/O  processor using  registers. timing, control, temporary storage, routing, command translation, and interfacing (internal and external) to perform I/O operations. Timing  Circuits As  we  discussed  in  the  memory  section,  timing circuits  also  will  provide  the  enables  to  manage  the  I/O control  circuits  used  for  I/O  operations. Some computers use the computer’s master clock and one or two other timing signals derived from the master clock to control the flow of data in I/O operations; an example of  this  is  the  timing  used  in  microcomputers.  Still  other more complex computers, such as mainframes and minicomputers,  rely  on  a  master  clock  and  main  timing circuits in the respective functional area (CPU, memory, or I/O) to produce and distribute timing signals to the I/O control circuits. In computers with an IOC, their I/O master clock and  timing  circuits  operate  completely  independently of the CPU timing. Their master clock is started when the computer is initially powered on or auto restarted. It can only be stopped or temporarily halted under 7-12