Here is a simple schematic of a RS-232 to ICOM CI-V adapter that
you can build yourself.  If you do not want to build your own, ICOM sells
an accessory that does this for about $90.00.

                   1N4001             +-------+
    +12 ------------|>|----+----+-----| 78L05 |-----+--------+
                           | +  |  in +-------+ out |        |
   Gnd  ---+              ---  ---        |gnd      | +      |
           |        22 uf ---  --- .05uf  |        --- 22uf  |
           |        16 v   |    |       ----       --- 16v   |
         ----              |    |      / / /        |        |
        / / /            ----  ----                 |        |
                        / / / / / /                ----      |
                                                  / / /      |
                                                             |
                                                             |
                                                             |
                        22uf +   1 +--------+16              |
                   +-----| |-------| MAX232 |----------------+
                   |         +   2 |        |15
           +---+-- | ----| |-------|        |-------------------------+
           |   |   |      22uf   3 |        |14                       |
         ----  |   +---------------|        |-----                   ----
        / / /  |             +   4 |        |13                     / / /
               |     +---| |-------|        |-----
               |     |     22uf  5 |        |12
               |     +-------------|        |-----
               |        22uf +   6 |        |11
               +---------| |-------|        |-----
                                 7 |        |10
    3  ----------------------------|        |--------+            To Remote
                                 8 |        |9       |            Jack (CI-V)
    2  ----------------------------|        |--------+--------------> (Tip)
                                   +--------+
    4  ----+                                                 +------> (Ring)
           |                                                 |
    5  ----+                                               ----
                                                          / / /
    6  ----+
           |
    7  ------------+
           |       |
    8  ----+     ----
           |    / / /
   20  ----+

 DB-25 (Female RS-232 connector)

        Parts list:

        qty     Description

        1       MAXIM MAX-232 (RS-232 to TTL level converter)
        1       78L05 (low power 5 volt regulator
        1       1N4001 (diode)
        6       22 uf at 16V capacitors
        1       .05uf at 16V
        1       DB-25 (Female RS-232 connector)
        1       Mini phone plug (to connect to ICOM Remote jack)