BINARY-CODED WORD INTERFACE.— The control signals in the ICCG interface are primarily in a binary-coded  word  format.  The  binary  words  are  shifted into and out of the crew ICS panels, the IRC panel, and the SLU on pairs of multiplex lines. The crew ICS panels and the IRC have unique binary word addresses that are identified by a roll call sequence performed in the SLU. Every 25 milliseconds, each crew panel and the IRC are interrogated for a change-of-status by the SLU. This change-of-status data is stored in the SLU until it is transferred to the general-purpose digital computer (GPDC)  for  permanent  storage.  The  GPDC  will  be discussed  in  a  later  chapter  of  this  TRAMAN.  The change-of-status data is then processed by the SLU to produce  mode  forcing  signals  that  are  sent  to  the appropriate  peripheral  and  ICCG  components. HARD-WIRE   SIGNAL   INTERFACE.—   The volume control signals and backup mode control and status signals are interfaced by separate lines between the components. These signals are analog voltages and ground  circuits.  These  signals  produce  changes  in  the components as the controls are adjusted or pressed without being processed first. ICCG Indicators Most of the indicators in the ICCG are either mode or function status indicators that come on amber and green. When the indicator comes on green, it means that the corresponding function is available for selection. When that function is selected, the indicator will turn to amber.  With  the  indicator  off,  that  function  is  not available for selection. On the IRC, the IFPM indicators will illuminate when  a  fault  is  detected  in  the  corresponding component. The S indicators on the crew panels will illuminate red when the secure mode of operation is selected  for  that  particular  radio  system.  The  indicators in the frequency selection section of the IRC come on red when frequency selection is available. Encoded and Decoded Word Format All the components in the ICCG, except for the three LS-602/AI  panels,  have  identical  binary  encoding  and decoding circuits. The encoding circuits transform a signal function into a binary word in the Manchester format for transmission to another component. The decoding  circuits  transform  the  Manchester  signal functions from another component into basic signal functions  for  application  to  processing  and  control circuits  within  that  component. Each of the components in the ICCG, except the LS-602/AI, have a unique binary word address. The component responds to an interrogation by the SLU only when  its  specific  address  is  recognized.  The  addresses are incorporated into the 36-bit ICCG word format. Each bit is a status or control function, or a part of the 5-bit  component  address  that  has  a  permanently assigned  slot  in  the  36-bit  format. The 36-bit words are serially generated and serially transmitted binary bit words. Each bit is either a 1 or a 0. A logic 1 corresponds to a voltage level between 5.0 and 8.5 volts dc. A logic 0 corresponds to a voltage level between -0.5 and –1.5 volts dc. ENCODED WORD FORMAT.— Encoded word format  is  setup  for  36-bits  that  are  either  status/control function  information  or  component  addresses.  Bit  1  is the control bit and is always a 1. Bits 2 through 6 are the address bits. Each com- ponent has its own unique binary configuration. One example of this is that the SLU recognizes the binary number 01010 as the pilot crew ICS panel. Should this configuration show up in bits 2 through 6, then the SLU will process on the command data from the pilot ICS panel during the 36-bit word cycle. Each component address word is designated by the decimal equivalent to its binary value. With the above example, the pilot ICS panel address 01010 is equal to decimal 10. Therefore, the pilot ICS panel designation is word 10. Bit 7 is the tag bit needed for binary word house- keeping. It is always 0 for encoded words. Bit 8 is the enter bit for binary housekeeping. In the encoded words it is always 1. Bits 9 through 34 are the command functions, status, or spare bits. Bit 35 is a command function, status, spare, or set-zero housekeeping bit. Bit 36 is the parity bit used for self-check in the binary  circuitry.  This  system  uses  the  odd  parity  check. If there are an even number of 1’s in the first 35 bits, bit 36 will be a 1. If the total number of 1’s in the first 35 bits is odd, bit 36 will be a 0. When a component receives the  36-bit  encoded  word,  its  decoder  checks  the  parity by counting the 1’s. If it comes up with an even number of 1’s, the word is not processed and a BITE indicator is  illuminated  on  the  component  that  transmitted  the faulty  data  word. DECODED  WORD  FORMAT.—  The  decoded word  format  is  similar  to  the  encoded  word  format  with just a few differences. Bit 1, bits 9 through 34, bit 35 and bit 36 are the same as in the encoded word. Bits 2 1-5