they can complete a full cycle. The decoding process is repeated,  causing  another  derived  clock  pulse  bit  and another  derive  basic  binary  word  bit  to  be  generated. When a Manchester bit is a binary 0, it cannot reset the  timers  through  the  inverter.  The  4.15-microsecond timer times out and produces a binary 1 at one input of the OR gate. The OR gate output is a binary 1 that represents  the  next  derived  clock  pulse.  Since  there  is  a binary 1 at one input and a binary 0 at the other input of the AND gate, the resulting output is a binary 0 that represents the next derived data bit. The 8.3-micro- second timer is still running because a binary 1 has not been produced in the Manchester word. The 8.3-micro- second timer times out and produces a 1 on one input of the NAND gate. The other input is a 0, which produces a 1 at the output. This 1 produces a 1 at the output of the OR gate, which represents a 1 for the derived clock pulse. Multiplex  Transmission Multiplex transmission data consists of 32 roll call words with a period of 800 microseconds for each word. The total period of time required for all the words is 25.6 milliseconds. Therefore, any one of the specific roll call periods occurs every 25.6 milliseconds. A roll call word consists of an inhale word and an exhale word, each being  400  microseconds  long.  Each  inhale  and  exhale word consists of 48 clock intervals of 8.3 microseconds each.  These  clock  intervals  correspond  to  data  bits.  Of the 48 bits, 6 bits precede the 36-bit Manchester word and 6 bits follow the word. This means that there are 12 bits between the inhale word and the exhale word, which totals 79.6 microseconds. This period of time allows the component  to  prepare  itself  to  receive  or  transmit  data. The SLU controls the ICCG. The roll call for the communication systems is generated there. Between the SLU and the other components of the ICCG, the exhale word is a status word Between the GPDC and the SLU, the exhale word is also a status word. The inhale word between the SLU and the other components of the ICCG is  a  command  word  that  tells  the  SLU  to  change configuration  or  frequency. The  status  is  the  configuration  that  the  com- munication systems are in at any specific instant, and is indicated by the color of the switchlight (amber, green, red,  or  dark).  A  configuration  change  occurs  whenever a  switchlight  is  depressed.  For  example,  changing  HF USB to HF LSB is a configuration change. Each component in the ICCG has a digital control section that controls all data entering or leaving the component.   The   IRC   and components that respond to the  SLU  are  the  only more than one roll call address. In contrast, the crew ICS panel only has to respond to one roll call address. Because of this, the crew  ICS  panels  use  comparators  instead  of  input register  decoders.  The  address  logic  is  hardwired  into the  aircraft  cable  connectors  for  each  crew  ICS  panel. This  allows  only  one  address  to  compare  true  at  each station,  which  makes  the  crew  ICS  panels  inter- changeable. Roll Call The  ICCG  logic  flow  and  roll  call  sequence  are described in the following text. ROLL CALL 0.– Roll call 0 is a spare on both the inhale  and  exhale  words.  When  the  800  microseconds have elapsed, the roll call generator produces roll call 1. ROLL  CALL  1.–  The first part of roll call 1 is exhaled from the SLU. Roll call 1 informs the GPDC that a change in configuration or status has occurred since  the  last  roll  call  1.  The  GPDC  buffer  and/or multiplex  lines  (port  2)  receives  the  exhale  word  from the SLU. There are three components of the ICCG hooked up to port 2. The IRC is the only ICCG com- ponent that recognizes roll call 1, and it processes the roll call through the digital control section, line receiver, and inhale word register. In the inhale word register, the Manchester  word  is  decoded  into  the  clock  pulses  and the data word. The roll call is matched against the address, and the decision is made whether or not to proceed  with  the  processing.  The  other  two  components are processing the roll call 1 at the same time, but because the address will not match, only the IRC will continue  processing. In the IRC, the derived data is sent to the input register  under  the  control  of  the  derived  clock  pulses. Word validation begins at this time. As part of the word validation process, the tag bit is examined. The tag bit of roll call 1 is a binary 1 that identifies the word as a status word from the SLU. A tag bit identification word in the IRC is sent to the inhale/exhale word gate. At the same time, the roll call 1 is sent to the exhale word inhibit gate that starts a 500-microsecond timer. When the timer times out, the exhale AND gate is enabled and the data word  is  shifted  into  the  exhale  word  assembly  register. The second part of roll call 1 is generated in the IRC. The data originates in the exhale word generator, and it represents  the  HF  configuration.  The  configuration  of the data bits in the exhale word register is shown in table 1-2. Data bits 15 and 16 are USB and LSB. When the USB/LSB  switchlight  is  depressed  to  change  from  USB to LSB, a pulse is generated that sets the bit 16 one-shot circuit. As long as the switchlight is depressed, the 1-8