TM 1-1520-218-10 3C-172 t.    Communication Radio Control. (1)   Communication  Radio  Control  Overview.   The     FMS-800    provides    control    of    the    following functions from the CDU for the ARC-210 V/UHF radio. 1.   V/UHF radio mode selection. 2.   V/UHF radio squelch, bandwidth, tone, and modulation control. 3.   V/UHF radio scanning operation. 4.   HAVE    QUICK    I/II    function    control, including MWOD and FMT list selection,   time   synchronization,   date entry, MWOD verification, and SINCGARS control functions. In  addition,  the  flight  displays  provide  heads  up control and display of the communication radios. Communication    radio    frequency    selection    is available via the communication page by selecting the COM  function  key  of  the  CDU.    The  V/UHF  control pages    provide    the    basic    radio    control     features.   Specialized  pages,  such  as  the  V/UHF  HAVE  QUICK II setup pages and SINCGARS control pages, are also available. If  the  FMS-800  cannot  interface  with  a  radio  for any reason (i.e., LRU failure, data bus failure, etc.), a check mark () will be   displayed to the left of the title line of all pages corresponding to that radio.  A   will also    be    displayed    on    the    communication    pages adjacent to the preset number of the LRU. Power  to  the  communication  radio  is  controlled via the power pages. The     FMS-800     also     has     provisions     for     an external,  crew-activated  emergency  mode  switch  for setting     all     communication     radios     to     emergency frequencies, if installed on the aircraft. (2)   V/UHF Radio Control. (a)   V/UHF   Frequency   Selection.      The crew    may    tune    the    V/UHF    radios    by    frequency, callsign, maritime channel, or preset number.   Frequency     tuning     is     performed     directly     on     the Communications page by entering the desired frequency in the scratchpad and pressing the channel selection line select key.  Refer to Figure  3C-124 and Table 3C-86.    A  valid  frequency  is  entered  as  two  to three  digits  followed  by  up  to  four  decimals,  followed by A, AM, F, or FM to define the modulation type.  An M  is  displayed  as  the  preset  number  to  indicate  the frequency  was  entered  manually.    Possible  ways  of tuning    the    communication    radio    are    with    manual frequency selections (including frequencies, net identifiers, or maritime channel entries), preset callsign entry,  preset  number  selection,  or  airport  frequency selection. Figure 3C-124.  Frequency Control Communication Page Table 3C-86.  Frequency Control Communication Page Procedure NO. DESCRIPTION/FUNCTION 1 Pressing  the  function  key    COM  will access the communication page. 2 Enter airport identifier and access the V/UHF airport frequency page. 3 Enter preset callsign or display airport callsign. 4 Enter frequency or channel. 5 To access preset list. 6 Indicates preset number. 7 To access the V/UHF control page. 8 Recall frequency to last tuned. The   crew   may   also   tune   a   V/UHF   frequency using the scratchpad of any CDU page and the  QUICK TUNE push button, located on the pilot's and copilot's control  yoke.    Enter  any  of  the  following  into  the  CDU scratchpad  and  press  the   QUICK  TUNE  push  button to tune the radio. 1.   A  valid  V/UHF  frequency,  channel,  or  net identifier. 2.   A   valid   callsign   for   a   V/UHF   frequency located in the preset list.  This does NOT include airport frequency callsigns.